Strange Noise - help needed pls

[jimbobery]

Bit of a weird one that I'm hoping someone can help with. Unfortunately I think this could be interpreted in lots of ways but here goes...

When I brake from speed, not hard, but say stopping for a roundabout I get what can only be described as a noticeable transmission whir. When I let off the brake it stays for about a second and then goes. But it doesn't happen if I slow to a stop without braking, of if I brake very lightly.

Some facts..
· Pretty sure its not haldex related, it happens in gear, out of gear, clutch dipped, handbrake up one notch, so I think some of those would disengage haldex
· I drove to town with two people and it wasn't happening, but then loaded up with 4 bags of gravel and some bricks (both totaling about 100kgs), filled up with 55 liters of fuel, only after this did it start happening
· I had a brake fluid change yesterday
· I have a snapped rear spring, but I think its only at the end and hasn't changed my height
· I've not got any VAGCOM error codes
· The noise hasn't continued to occur after I've emptied the boot and only had 1 extra person in the car
???

 

[jimbobery]

Bit of an update... I didn't get enough gravel earlier, went out to get four more bags with just me in the car and I couldn't get the whirring noise to happen on the way to b&q, put the four gravel bags in the boot and on the way home I'm able to make the noise occur again! WTF??
Why is 100kgs of weight in my boot doing this?

 

[jimbobery]

no-one got any thoughts on this?

 

[HTC]

I would say that the whiring could be from the rear brake discs. When the boot is loaded up the rear aportioning valve for the brakes sends more pressure to the rear calipers. You are probably just listening to the effect of more pressure on the rear system or even the system as a whole as you'll be using more brake effort to slow the car with the extra weight. It's alos possible with the extra pressure at the rear that you could be simply scrubbing off an area of the disc that hasn't been used for a while.

One further thing, check the pads haven't worn down too much front and rear.

 

[Sanj]

I agree with HTC

Mine whines at about 15-20mph, ive been told its the rear brake discs that cause this.

 

[jimbobery]

Thanks for the response guys. Lighter braking didn't cause the whirring, so its making sense; I'd never heard of the apportioning valve though!

Brake pads were confirmed as ok by Audi the day before, not that that should be taken as gospel though, I shall be checking them myself soon.

Thanks again, it has me worried at first, I was scarred it was Haldex related.

 

[fingermouse]

Do the rear discs have a bit of a lip on them ?? If the corrosion on the edge of the disc is quite big then you could get a noise as it rubs the side of the pad.

 

[jimbobery]

Yeah, the rear discs haven't been replaced for a few years as far as I can tell so they do have a lip.

I've been doing some more reading on this and it actually mentions this in the owners manual under the section on ESP. It says that ESP will change the braking force from the front to the rear under different load situations, less braking force to the rear when there is a light load to prevent locking up at the rear, and more braking force when the rear is loaded with weight. The user manual says there is a noticeable noise when braking force is being controlled by ESP.
Having said that, I think the lipped rear discs are likely to be making some of the noise if they are receiving more braking force than usual, this was the first time I have ever put anything of any serious weight in the boot.