B6 S4 - Buzzing/Resonance between 2-3k, with odd symptoms :-(

[VaguelyAmused]

Hi all,

It's been a 6 month costly roller-coaster of ownership so far, 2004 B6 S4, and this latest issue has me (and the garage) at a loss. I'm now pitching the heart against the mind to decide how much longer to really keep going before calling it a day and retiring her.

A recent "development" in the symptoms makes it probably specific enough an issue to ask you lovely people if anyone has come across this before - its really a plea to save what remains of my hair! I don't think I can bring myself to walk away from her without knowing for sure what it is but that in itself may break me.

Anyway less of the X-Factor style prologue, on to the issue:

I get a buzzing noise from the front/engine area that comes in most noticeable at 2100rpm and then steadily gets worse as the revs rise until 3200rpm when it then goes away, through the rest of the rev range upwards she sounds absolutely fine. When I then let it drop down through the revs again, the noise doesn't come back until they drop to 2100rpm. When changing up, if I blip the throttle to above 3200rpm to kill the noise and then keep it above 2100rpm through the gears you would think it is all fine. Let it drop below 2100rpm and the noise comes back, up until 3200rpm. Seems to be from the left hand bank of the engine as looking at it, right hand sounds fine (although experience with the alternator bearing failing teaches me horrible, horrible noises can sound like they are coming from somewhere they aren't). Garage has had a look, sump off, stethoscopes and boroscopes out but no damage found, comment was just bearing shells look worn (engine has done 147K, but timing chains/tensioners at 125K).

I'm not sure if the noise only comes in at 2100rpm, or whether being in the cabin is sound proofing enough not to hear it at lower revs, I need to get out and around the engine bay with a mate on the gas pedal). Certainly when hitting 3200rpm to clear the noise and dropping down the revs, 2100rpm is very definitely the point the noise "switches" back on.

Various things pop up in the search, sheered tensioner bolt again, CATs, exhaust (its a Milltek resonated cat back), hyrdaulic lifters, timing chain tensioners but videos I can find on youtube don't really match with the noise I'm getting, and the garage checked for sheered bolts and would have checked the CATs and obvious things (surely, before going as far as taking the sump off!?) The noise itself is quite high frequency, and quite "growly".

Recent alternator change including tensioner and pulley, and then back again for a sheered tensioner pulley bolt a few weeks later. This issue came about 2 days after that :-(

There are a few specialist garages that tune Audi's near me (Poole, Dorset) so I may take it in and see if they mind coming out in it with me for a minute and give me their thoughts, but if anyone here has come across these sorts of symptoms before that could shed some light on what is going on, and perhaps more importantly has had the patience to read through my waffle I would owe you my sanity and my hair.

Thanks all
Chris

 

[cobraBLACK]

It may be a coincidence but the fact it started just after the alternator work seem suspicious.

Does it do with the clutch disengaged?

Is it just a noise or are there any other symptoms?

I've been using Independent Garage Services (IGS) in Eastleigh (J13 of M3 or J5 of M27) since I got my S4 and have been very happy with their service. They've just done my timing service / top-end rebuild because they know what they're doing.

 

[QuattroCalum]

Have a look at this Chris, it could be your answer.




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[VaguelyAmused]

Guys, thank you for the replies and thoughts, I type this giddy with hope!

cobraBlack I completely agree it has been really hard not to be super cynical about the garage and I occasionally berate myself for continuing to take it back there. They treated my Golf well (2.8 v6 4motion, which I still regret selling) so I do trust them - it makes it harder when they do the alternator and then not long after the bolt shears (at my cost btw) hmmm.

The noise is present whether clutch engaged or not, I wondered about DMF but speaking to someone at work who had that go getting it into gear was a PITA and my gear change effort is normal.

QuattroCalum that brings me onto your suggestion and the reason I am giddy! You may have it absolutely spot on. Just come back from a friends trying to get him to record a video of the noise (it came out crap, all you can here is my annoying voice, wouldn't make a good youtuber). On the way back the noise completely changed, or rather when it could be heard changed. It is now only audible in the cabin between 1600-1800rpm.

I'd almost concluded it was the cam adjusters until this point, the way the noise switched on and off (assumed something to do with vvt), but with the change in when it could be heard my optimism rose. This combined with now at about 3krpm I get a sort of "whaa whaa whaa" beat frequency from the exhaust (I think) - kind of has to be some sort of resonance somewhere.

To the point I have just come in from poking around at the exhaust to see if it was loose on a broken hanger or something (it isn't, it seems sturdy) but I guess just poking it with a stick wouldn't pickup on a bad flexi joint.

The reason for the two happy dancy people - I bought at a bargain price two milltek high flow sports cats/downpipes for her the day I bought her (took a detour driving her home to pick them up) but have never fitted them because of the ongoing problems elsewhere. I'd also made up my mind that if the problem was engine related I was getting rid, the only thing that would have me keeping her would be a non-engine related issue.

I think, please say I'm right, that the milltek sports cats combined with the milltek cat back will replace the potentially faulty flexi joint, so basically a job I thought would be £ks may just be labour!? I think that calls for another

QuattroCalum if this ends up being the problem (and the video noise certainly matches, just perhaps not the same rev range - thats resonance for you I guess) then I don't know how you feel about male-male contact, but I owe you a big hug (and a beer)!

I'll keep you posted.

 

[VaguelyAmused]

Apologies, just re-watched the video and realise that although a good excuse to swap in the millteks if this is my issue, the more important thing is to make sure they are properly supported. It doesn't suggest the flexi's have so much failed more just got weak enough to let the exhaust rattle around.

Still sounds optimistic, I imagine they are the originals and have done 147k. Thanks!

 

[QuattroCalum]

Any progress with the diagnosis of the noise.


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[VaguelyAmused]

I am hoping over the course of this coming week to get to the bottom of it. Time just ran out in the lead up to Christmas with everything else going on. I got slightly less optimistic that it was the flexi-pipes, as it seems on the B6 S4 there is a support bracket welded on the down pipe right next to the flexi joint but it has to be something along those lines however I decided against driving it the 300 miles up North to see family just in case - I'd hate to do more damage to it (ps 300 miles in a Mk1 MX5 was not as tedious and back breaking as I thought it may have been!).

I'll definitely be updating this thread as and when progress is made.

 

[rjm180]

VaguelyAmused, What was the outcome, hope you got it sorted in the end.

 

[VaguelyAmused]

Hi all,

Apologies it has been such a long time before updating this thread. I'll be honest she sat parked up on the driveway for 2 months, I just couldn't face or really afford at the time to keep throwing money at her chasing the problem and it was getting to me.

Last Friday however she got booked in for a road test and diagnostics at Audi themselves. They have found the problem!

The problem with the problem is it leaves me raging at the moment with the original garage. Its worth a quick summary of the original garage's involvement first:

- Went in for a horrible mechanical "engine" noise. Ended up being the alternator bearings so alternator, belt and tensioner were replaced
- Went back in a few weeks later for another noise. Ended up being a sheared tensioner bolt (yes, the alternator belt tensioner) so this was replaced
- Went back in again a few days later for yet another noise. Garage investigated initially and couldn't find anything, then took the sump off to check what they could, all ended inconclusively
- She then sat on the drive for a few months

So, what is the problem... a sodding alternator bolt! 5 stars to the Audi service, I received a link from "AudiCam" to a video. Shows that when they put tension on the alternator with a screwdriver the noise goes away. Most unbelievably, Audi found the bolt, laying in my front bumper lip!

I can only assume that the bolt was not torqued correctly, and that the initial noise through a larger rev range was whilst the bolt worked itself loose and the noise as it ended up being (in a very specific rev range) was once the bolt had worked its way fully out.

Of course, the whole front end comes off again so the bolt can be put back in.

I am absolutely appalled by the original garage at the moment. I'm trying to stay calm headed but will be speaking to the garage to claim a lot of the additional cost back and if they don't play ball will be a legal battle I think, which I am more than ready for! I won't name garage names yet, I don't want to do anything right now that could risk any legal claim but I am based in Poole, Dorset so if anyone local wants to know the garage name perhaps PM me?

Thanks for the suggestions and support

Chris

 

[QuattroCalum]

Hi all,

Apologies it has been such a long time before updating this thread. I'll be honest she sat parked up on the driveway for 2 months, I just couldn't face or really afford at the time to keep throwing money at her chasing the problem and it was getting to me.

Last Friday however she got booked in for a road test and diagnostics at Audi themselves. They have found the problem!

The problem with the problem is it leaves me raging at the moment with the original garage. Its worth a quick summary of the original garage's involvement first:

- Went in for a horrible mechanical "engine" noise. Ended up being the alternator bearings so alternator, belt and tensioner were replaced
- Went back in a few weeks later for another noise. Ended up being a sheared tensioner bolt (yes, the alternator belt tensioner) so this was replaced
- Went back in again a few days later for yet another noise. Garage investigated initially and couldn't find anything, then took the sump off to check what they could, all ended inconclusively
- She then sat on the drive for a few months

So, what is the problem... a sodding alternator bolt! 5 stars to the Audi service, I received a link from "AudiCam" to a video. Shows that when they put tension on the alternator with a screwdriver the noise goes away. Most unbelievably, Audi found the bolt, laying in my front bumper lip!

I can only assume that the bolt was not torqued correctly, and that the initial noise through a larger rev range was whilst the bolt worked itself loose and the noise as it ended up being (in a very specific rev range) was once the bolt had worked its way fully out.

Of course, the whole front end comes off again so the bolt can be put back in.

I am absolutely appalled by the original garage at the moment. I'm trying to stay calm headed but will be speaking to the garage to claim a lot of the additional cost back and if they don't play ball will be a legal battle I think, which I am more than ready for! I won't name garage names yet, I don't want to do anything right now that could risk any legal claim but I am based in Poole, Dorset so if anyone local wants to know the garage name perhaps PM me?

Thanks for the suggestions and support

Chris

Glad you have the problem solved now but that's very poor service from the first garage, you're right to be angry.
It's the simplest job ever, how can they go wrong with this.

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[VaguelyAmused]

Cheers! It is nice to finally have her back and not making silly noises

I am left with one final noise, and for the life of me not sure whether it was there or not before all this work but the Audi mechanic who came out with me on the road test said it was normal and described the noise before we even got started so I'm inclined to believe him. Its just a bit annoying which is why I would have thought I'd have noted it before.

Cruising around 3100rpm there is a very obvious low "brr, brr, brr" at a frequency of maybe 1-2 "brrs" a second. The frequency does increase as the revs increase (not by much, certainly not linearly to the rpm) but the tone also becomes higher and less noticeable. I'm not really worried about it from a real problem point of view it just spoils the exhaust note a little when giving it the beans and climbing through the gears. Its hard to compare with videos on youtube as they are usually just drive byes or standing starts but I don't think I hear it in those.

I may take it to an exhaust "specialist" because to me it seems related. I am now itching to put the sports cats on but don't really want to make the brr'ing any more obvious or louder.

 

[cobraBLACK]

That doesn't sound normal. Can you get it in a video?

 

[VaguelyAmused]

I suspect so yes, let me go out and try - if only for making sure I am not going mad!

 

[VaguelyAmused]

Hi guys,

Hopefully the noise comes through, it is a little hard to hear through the general background noise in the video, I wanted to show the revs in the video so it may not be the best direction for the mic. Far more noticeable in person. I second guessed myself and thought maybe wheel balancing or flat spot but its rpm related not speed related.



Its that sort of "thing" though, a hum almost as if you driving on alternate thin layers of concrete and tarmac.

Cheers