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!
1987 560SL 109,000 miles
2001 E320 103,000 miles
2007 E350 32,000 miles