Mercedes-Benz W201 rear end whine and hum
What causes the rear end whine or hum on the Mercedes-Benz W201?
The source of the noise is often the propshaft support bearing or its rubber, a wheel bearing, or worn gear contact in the rear end (differential). The noise does not necessarily come from the rear end itself, so before replacing the rear end it is worth checking the propshaft joints and support bearing and the rear end oil level.
How can you tell whether it is a bearing or the gears?
If the noise disappears when you lift off the throttle, it points to worn gears and incorrect gear contact. You can listen for a bearing by lifting the rear end into the air and spinning the wheels. Metal glitter in the oil tells you a bearing has started to wear.
What can be done about the whine?
Replacing the propshaft support bearing is an easy and inexpensive first step. If the noise is from the rear end, the whine often goes away by rebearing the rear end and adjusting the gear backlash, but worn gears require replacing the rear end. Adjusting the rear end is best left to a professional.