Potential brake problem?

First of all: full marks for the show. I try to listen to it regularly - even when it’s just via podcast.

I’m currently having a little bit of a problem with my A-CLASS Merc (I don’t know if it’s sold in the US but it’s comparable to a jazzed-up Golf-type vehicle). After about ten to fifteen miles of driving, I hear a metallic grinding noise coming from the wheels. The frequency changes with speed, so I’m suspecting the brakes. What’s interesting though is that this speed-dependent rhythmic noise is only audible up to around 50 mp/h after which it changes to a whining sound independent of speed. The whole thing goes away beyond 60 to 70 mp/h but it just may be drowned by the engine noise then.

The rotors seemed to be OK upon first inspection but I haven’t yet checked the pads. Both are only approx. 6,000 miles “old” though. The car itself has approx. 90,000 miles on the clock.

As this problem is somewhat intermittent, the dealership which I normally use to get the car serviced cannot detect much here.

Any thoughts / ideas would be greatly appreciated. Let me know if more information is needed.

Have you considered the possibility that you have one or more bad wheel bearings?
Before this causes an accident, I strongly suggest that you check all of the wheel bearings.

If this was a FWD vehicle, CV joints would be a vague possibility, but since this is a Benz, I assume that it is RWD. Have your wheel bearings checked.

PS: Almost forgot: The noise increases when steering to the right side and goes almost away when steering into the opposite direction. Braking eliminates the noise altogether.

This convinces me even more that you have a bad wheel bearing–most likely the one in the left wheel hub. However, both of the front wheel bearings should be checked.

Being that this is an M-B, the parts will not be cheap, but this is not something that you can afford to defer, as it is a definite safety issue. I assume that you know what would happen when a bad bearing suddenly seizes up.

Thanks for the quick response and the hints! This is what I really like about this community.
The car is actually a FWD with the engine partly under the passenger compartment. More details for example at http://en.wikipedia.org/wiki/Mercedes-Benz_A-Class#Specifications.
I’ll have a mechanic look at the bearings asap.

I did not know that M-B used FWD technology in any of their vehicles.

go to a quiet parking lot, near a shopping mall.

drive along side the building windows down, radio off. when you’re driving one way, is the noise louder from either side? when going say 15 to 20 let up on the gas. then try touching the brakes. does the sound disappear? does it do the noise when braking too? try both sides.

after a drive, get out and feel the hubs of the wheels. is one side hotter/warmer than the other?

If the noise goes away during braking I would definitely suspect a bad bearing.

The sound echoing off the wall will help you figure out which side it is on. It should be considerably louder on the side with the bad bearing.

I am surprised a genuine MB shop couldn’t figure this out!