My 1983 300CD started to make a humming sound. It is constant and "all the time" It is speed dependant, where the pitch changes with the vehicle speed, but not the engine speed. It is clearly audible, but not overwhelming, almost like I have noisy offroad tires on it. I think it may be comming from the front of the vehicle, and may be a wheel bearing? Otherwise the rear, where it could also be a wheel bearing, or driveshaft issue? Or maybe I am off base entirely.

What do you think?
What is it?
Is this something I can fix in my backyard with ordinary tools?

Mark

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1983 300CD 245K
Running WVO blends