560SL whistle/squeal under acceleration
 

1987 560sl has a squeal/whistling type noise on acceleration. Most noticeable when at 20mph and accelerating to move into a fast lane or adding power for a hill. My mechanic has been stumped by this one--but he does not have a dynameter and cannot recreate the noise on the floor even though he hears it when test driving. It is not the belts, though to my ear it sounds like a belt squeal. If it is a failing bearing it wasn't discovered in the shop using stethoscopes. Possibly a very small vacuum leak? I agree that the next step should be to find a shop with a dynameter, but if anyone has had this problem I'd be interested in hearing about it. Thanks!

John C
Oakland, CA

JohnC,

I had a similar symptom on my 240D when it was relatively new, and it turned out to be a pinhole in the exhaust system that would, under certain rpm and throttle conditions, whistle, and very loudly at that. I found and patched it, but the patch did not last too long and I ended up replacing the section of pipe with the first near 90 degree bend. That took care of the problem and even when that pipe began to fail I never got the whistling back. Hope that helps, Jim

JohnC

I have a similar noise in my 380SL. But only when cold. Once it warms up, the noise goes away.

JimSmith could be right as to the pinhole in the exhaust system. I just had a new convt installed. Did not do it prior.

Hope it help.