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 and what's the fix.

Thanks!!

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1973 280 - Sold
1980 300SD - Sold
1982 240D - Stolen
1988 300E - Sold
1989 260E - Sold
1989 560SEL
1994 E420 - Sold
1997 E420
2005 CL500