Facelift S3 rear humming sound.

[benabbyg]

Pleased to have found this forum.
I'm hoping it can be a useful source of info, plus perhaps I can help one day.
I've a 2014 S3 which has recently started making a 'humming' noise from the rear. It's regularly serviced.
My local garage (not Audi) has checked the wheel bearings, and they seem ok. Tyres look ok, no odd shapes in the profile. It's a strange one as the sound is louder as I free-wheel/roll forward, without accelaration, even at very low speeds 2-3-5mph, but as soon as I apply even the smallest amount of throttle the sound/humming reduces by 50-70%. I thought it was wheel bearings but at such low speeds it did seem a bit odd.
Any advice would be very much appreciated.

 

[HertS3]

Could be your rear differential, mine did that before it conked out

 

[Leevr]

As above, Haldex differential can be problematic if not serviced regularly. Audi tend not to remove the pump and clean the screen, not classed as a filter. First thing get an oil change and filter service/ clean by an independent. New pumps are around £220 if it's broken.

 

[HertS3]

@Leevr just to set the record straight - the Haldex system (the on-demand 4wd system) is located within the Final Drive which contains the Haldex and rear differential systems next to each other. Just so we don't confuse the OP

 

[benabbyg]

Thanks everyone, have to admit the last service Audi did for me, I told them not to bother with the rear oil! It's only done about 5,000 miles since then, hoping that hasn't caused it to fail so soon!
Would an oil change & filter do anything if I sorted it out asap.
Leevr you mention new pump at around £220 - would you know if this 'humming' could be the pump packing in? The thought of new rear end is frightening!

 

[HertS3]

It's actually not as bad as it sounds, get a used one from a breaker for around £300 on eBay, you do need new Haldex and rear diff oils though plus some labour to change it over. You can keep existing Haldex ECU so no programming needed.
If it turns out that you do need one give me a shout, I did a lot of research on it when I needed one.
Still got an ongoing complaint with the Motor Ombudsman against one of my local Audi dealers over it!

 

[Leevr]

Thanks everyone, have to admit the last service Audi did for me, I told them not to bother with the rear oil! It's only done about 5,000 miles since then, hoping that hasn't caused it to fail so soon!
Would an oil change & filter do anything if I sorted it out asap.
Leevr you mention new pump at around £220 - would you know if this 'humming' could be the pump packing in? The thought of new rear end is frightening!

Unfortunately I couldn't hear mine making any noises, got a milltek system that quite loud. My first issue was that at speed when overtaking I would get a violent shimmy from the back end. At a decent legal ish speed. I would also get the front wheels hopping violently on hard acceleration from a standstill.

 

[benabbyg]

Thanks HertS3 - I appreciate the advice, been reading of horrors like £3-4k to sort the rear out!
I've a local AVW specialist not too far away, I'll pop over to speak about oil/filter change, plus they can take a drive in it. But always good to have some prior knowledge on the issue.

 

[HertS3]

Thanks HertS3 - I appreciate the advice, been reading of horrors like £3-4k to sort the rear out!
I've a local AVW specialist not too far away, I'll pop over to speak about oil/filter change, plus they can take a drive in it. But always good to have some prior knowledge on the issue.

My rear diff apparently had no oil in it for over a year, according to Audi. They blamed independent mechanic of draining by mistake instead of Haldex. Get your mechanic to check whether you've oil in the rear diff, it's not a sealed system (has vents on the top), so how Audi can say it's 'sealed for life' is beyond me (plus how come they sell the rear diff oil on its own?!).
Audi quoted me £3,500 or more for a new part by the way.

 

[s5joe]

Mine is doing the same but it is speed dependant and is getting louder on lower speeds i would say from about 30mph

 

[HertS3]

I'd get the rear diff checked out

 

[s5joe]

I'd get the rear diff checked out

Whats the best way of doing that

 

[HertS3]

Ask a mechanic, I wouldn't know

 

[benabbyg]

Local Audi specialists have investigated the rear noise. Not tyres, not wheel bearings, were able to hear it whilst on the ramps, they’ve said it looks life diff is the problem!!!
Part only available from Audi, £2500+vat!!! plus fitting, approx £600! Just can't believe it!
They’re going to check it further tomorrow…just incase!, but not looking good.
I’ve not asked them yet, but wondering if a thicker oil grade is an option? Ok not the proper fix, but would give me some extra time.
Would a thicker oil be an option?

 

[HertS3]

You know where to tell them to stick it! eBay should have some available to buy second hand for around a tenth of that price, Audi won't fit a used one for you but an independent should do it for an hour's labour or so plus the cost of rear differential oil and Haldex oil, it's just plug and play (if you keep the existing Haldex control module). You'd need to find out which revision of the part your car has of the Final Drive - this is rear differential and Haldex (at the end of the part number, e.g. F, G, H, J, K etc, latest I think is T, youll be able to see it on the quote from Audi), you can go newer but not older than what you had.
Happy to advise (with my limited layman's knowledge as someone who has been through this) if you want to go down this route.
Hope it goes well tomorrow.
By the way, it's untested but I'd imagine that Audi extended warranty wouldn't cover the part, though there's an argument here that's it's an original Audi part so as long as it's installed to Audi's specification it should be covered. Hopefully I'll never have to have this argument lol

 

[benabbyg]

HertS3 - thank you for the supporting words. I'll begin my eBay search!

 

[HertS3]

No worries, glad to help out.
eBay sellers were very keen to haggle as they've obviously had these parts knocking about for a while (not something that usually goes wrong), so if you can hold out they should give you discounts. Message sellers asking age and mileage of vehicle it's come off etc, that might prompt them or you could just try to haggle from the outset.

 

[benabbyg]

You’re amazingly helpful – appreciate it very much!
It’s with an independent garage now, not Audi, but they do specialise in Audi.
I’m doing some research to try and understand what’s possibly needed. I’ll have a chat with them tomorrow to learn more, but always handy to be pre-informed.
From the units on eBay I see most have the Haldex still attached. I guess if mine is ok then that can be swapped over? or is the re-coding a pain if I leave it on it? But as you say I need to check the part number (will take photo tomorrow, hope I can see the label/part No. whilst it’s on the ramp) You mention the oils, that’s fair enough, surprised (and pleased) to hear the change should only take about 1-2hrs.

 

[HertS3]

Yeah it's not a big job as long as you're not coding in the new Haldex ECU. I think most come with it but you could possibly sell it, not sure what demand there is for them but I think they were asking for around £100 on eBay when I got mine a few months back. Not had any problems since

 

[benabbyg]

I'm learning....so I can just swap the Haldex ECU, no need to swap the Haldex unit also?

 

[HertS3]

Vice versa, the "Final Drive" unit (as Audi calls it) consists of the rear differential and Haldex systems, with the Haldex ECU connected to it but a separate unit. For an easy life, if your ECU is fine and the issue is with the rear diff (so the Final Drive), keep the existing ECU and no coding required, just replacement of the Final Drive.

 

[benabbyg]

One more question please.....you mention the correct part number letter, and not to fit anything older, if I'm keeping my ECU does the letter matter?
Thanks again!!

 

[HertS3]

The letter on the Final Drive part number (0CQ525050# where # is the revision letter) is the one that must be the same or newer, the Haldex ECU part number is 0CQ907554# where again # is the revision letter. If you're not replacing the Haldex ECU then the revision of the ECU doesn't matter to you. It may the same revision as the Final Drive but maybe not, but it won't matter to you. I think the Final Drive has to be the same or newer so that you can keep the Haldex ECU but not entirely sure, I just know that advice that I got from somewhere worked fine for me, I went from F that the car came with to L with no issues.

 

[benabbyg]

Ok, thank you, I'll find out what's on mine and compare with eBay items.
Bye for now - you’ve been incredible with your advice!

 

[Damo S]

Might also be a knackered prop shaft bearing. Im not sure how easy it would be to pinpoint the exact location since its all so tightly linked together.
Mine used to make a hum when reversing sometimes, like the rear pads / handbrake wasn't fully disengaged. I know it wasnt that because I tried leaving teh car overnight with the handbrake off and it still did it.
When servicing the haldex pump recently my mechanic noticed the rear prop shaft vibration damper coupling (donut) was split. Since that was replaced I haven't noticed the humming sound.

 

[benabbyg]

Thanks for the reply - wish it was the propshaft bearing - saw the metal bits that came from the rear diff oil today! magnet was covered - not good! It's the diff! So the search begins for a used diff, new Audi item is well beyond me!
Part code: 25BO CQ 525 010D

 

[Damo S]

oh no

 

[Liam Morris]

Thanks for the reply - wish it was the propshaft bearing - saw the metal bits that came from the rear diff oil today! magnet was covered - not good! It's the diff! So the search begins for a used diff, new Audi item is well beyond me!
Part code: 25BO CQ 525 010D

Hi mate, Not sure where you are based but i have seen some specialist independents before who try to keep stock of second hand units for things like these so there's every possibility there might be a V.A.G specialist near you that does the same! it wouldn't hurt to call any V.A.G specialist within close enough proximity to you just incase they happen to have one lying around!

Hope you get it sorted and doesn't cost an arm and a leg!

 

[HertS3]

Oh no, I feel you! Did you ever have your Haldex serviced elsewhere? I did (oil change) so they blamed the indy for accidentally draining the diff oil, as mine had no oil in it, apparently for over a year! I had hesitation from standstill from when I bought the car (3.5 years old) so I took it in to the Audi dealer for a check up, they found a leaking thermostat but no problem with Haldex. When I came back with knackered rear diff and I asked how come they didn't spot this when the car was in for a problem in that area, they said that they would never look at rear diff as it's 'sealed for life' (despite selling the oil as a separate part and the fact that the rear diff has tubes on the tube for air cooling, if it's not a sealed system how can it be sealed for life???
I reckon yours had the same problem as mine, oil has somehow disappeared/evaporated(?) causing the unit to run without oil and eventually filing the metal down inside. Also yours is older than mine (D, mine was F), note that they're on at least T by now! Why so many revisions of the part, smells like a problem to me. Audi don't care as it only seems to happen to a small number of customers (so far).
The lesson going forward now is to have the rear diff checked for oil when the car is in for servicing/engine oil change.
I hope you get it resolved shortly, let me know if I can help

 

[HertS3]

Might also be a knackered prop shaft bearing. Im not sure how easy it would be to pinpoint the exact location since its all so tightly linked together.
Mine used to make a hum when reversing sometimes, like the rear pads / handbrake wasn't fully disengaged. I know it wasnt that because I tried leaving teh car overnight with the handbrake off and it still did it.
When servicing the haldex pump recently my mechanic noticed the rear prop shaft vibration damper coupling (donut) was split. Since that was replaced I haven't noticed the humming sound.

By the way, when the car went in for the knackered rear diff they also found an issue with the propshaft, luckily that was replaced under warranty (though not so well, gave me the car back and the engine was thumping within 5 minutes and EML on, died on me when giving way on a roundabout on the way back to the dealer!)

 

[benabbyg]

Wow, you've been in the wars with yours! I agree the revision status does make you think why? Mine's only ever been to Audi, apart from recently to look into the diff problem! and both did have oil inside. It's so annoying why such a major failure can happen on a 50k miles car.
Still searching for a used part on eBay. Looks like it'll be a £375-475 spend on the part.
Silly question - but would you know if it matters if the diff has been removed from an Auto (mine is manual)
Yuo've been a star in providing some very useful advice!

 

[HertS3]

Hmm I'm not sure, I wouldn't think so but I'm not the person to ask. I would say if the part number is the same then it works?
Hopefully the lockdown will work in your favour, I found that items I watched on eBay were offered to me cheaper, as I said previously these parts tend to hang around for a while so breakers wanna shift em! My car was in with Audi for over a month whilst I argued with them and sourced another unit (which I had fitted elsewhere), then got the car back to find that they'd botched up the propshaft replacement (turned out to be a stuck magnet!).
I'm starting to think these diffs have an inherent design fault, if I'm correct many more people will be having these problems as the cars age. Hope I'm wrong!
Anyway my complaint is with the Motor Ombudsman now, it's taking forever

 

[benabbyg]

Good luck with the Ombudsman! I'll seek some info with the rear diff...
Would anyone know if a rear diff thats come from an auto would fit onto my manual S3 8V?
It has the same part numbers as mine - end letter is D on mine, the auto is H.

 

[HertS3]

I would have a chat with Martin at Unit 20 on 0151 33 66 888 / https://www.unit20.com/

He was recommended to me by @S32B and he told me what I told you! I suspect it doesn't matter, see https://www.ebay.co.uk/itm/Rear-Dif...Sline-VW-Golf-MK7-4Motion-TT-8S-/293050216679 for example (which I recognise from when I looked nearly a year ago - see what I mean about them hanging around??) which came off a diesel A3 but is still the same part number (newer than yours, F, which is what my car had from factory). Are you sure that your car is facelift (icon on subject of this post)? With the D variant I'm guessing it's a 2013-14 car hence pre-facelift (PFL).

 

[benabbyg]

Yes I'm thinking the same, part numbers match on an auto diff I'm looking at with a H (mine is D)
Mine is Jan 2014, it's the facelift.

 

[HertS3]

Jan 14 isn't facelift, mine's back end of 14 and is pre-facelift. You might be thinking of the older version 8P compared to our 8V? Facelift of the 8V was in 2016 or so

 

[benabbyg]

I see what you mean - my mistake, pic of mine attached.......but I guess everything is still ok with my search for the rear diff when I match the numbers.

 

[HertS3]

Don't worry, you get to learn these things hanging out on this forum! Yes, part numbers still good (hopefully), I'd phone that Martin and confer with him, he's very knowledgeable. Do your independent dealer that you took the car to not know the answer?