Okay here’s what I have…..a 1989 560SEL. When driving on level ground between 40 and 50 mph there is an odd sound VERY similar to a whistle buoy on the ocean. It only makes the sound when pressing the accelerator to maintain the speed. When I remove my foot from the accelerator pedal the noise stops.
What is causing this noise?
The expert may disagree, but I would check the idler pulley wheel the belt runs on. Could be a bad bearing.
Have you tried a forum search? The archive has a wealth of information.
Welcome, to take advantage of all the forum features, please re visit the 'Welcome to the Forum' tutorial sticky on top of the W126 page, as well as the two DIY stickies.
It will show how to search the forum (3 words min.), and has a link to the Russian MB site where you can run a VIN#.
Idler Pulley/Roller; AC Idler Pulley without Bracket; 15mm Bolt Hole
Also may need 1159900219 stretch bolt on some models. Verify that deep groove (66mm OD in groove) is on vehicle prior to ordering. 1 per car.