Most likely a wheel bearing. You can fix in you backyard. You can usually get by with simply repacking the current ones, but they are cheap, so ou may want to just replace them on principle. You'll need grease, channel locks, allen key (can't remember what size, 10mm?), and a drift and hammer if the races little "cups"that press into the hub and fit against the bearings) are scored and need replaced. They made my car sound like they were riding on really knobby tires.

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1989 300E 144K