I wanted to ask the same question.

Now that my car is quiet (I fixed the exhaust), I can hear whinning in the back. It doesn't change on accel or decel, so I don't think it's the diff. This is a lower pitched sound that develops as soon as the car is rolling. I have also noticed that it goes away while turning to the right. I'm thinking tires, or wheel bearings. Any guesses?

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Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)