ChuckinTucson

At freeway speeds, if I let off on the gas pedal to slow down a little (just coasting, not braking), there is a high pitched whining/humming like noise coming from the back of the car. Been doing it for awhile, but doesn't seem to be getting worse. It is very faint, nothing loud.

It's on a 2002 S500 with 92,000 miles.

Anybody got a clue what this might be? Differential?

cwallens

to me it sounds like the catalytic converter is clogged up.

eugeneC55

Is your car 4matic?

ChuckinTucson

No, it is not a 4Matic. Didn't even think of the catalytic converter. Car has 92,000 miles on it. Will check that out the next time it's in the shop.

eugeneC55

I had similar sound under similar conditions (when letting off gas at highway speeds) on my '08 S550 coming from the front (my car is 4 matic). Turned out it was caused by damaged joint of the prop shaft. If I remember correctly the explanation by the tech the noise had something to do with the joint being fully engaged when under the load (and not making noise) and then getting looser and making noise by damaged components when I would let off gas. In any case the noise went away after prop shaft was changed.

wallyp

The differential has a slight whine on my 2003 S430 with 225k miles. Changing the fluid made no difference, so I just live with it...