Rear Axle Noise

Hi,
I'm experiencing a noise from my rear axle. Its intermittent and only audible in at slow speed in 1st/2nd gear. If I'm rolling slowly down a hill
with the clutch in (engine disengaged from transmission) theres no noise at all. If I lift the clutch slowly to engage engine the noise appears. It only occurs under light load, either accelerating or decellerating and if I try to create a no load situation by being careful with the accelerator I can effectively make the noise disappear for a moment. The noise I get is obviously coming from something thats rotating and the frequency of the noise is proportional to the wheel speed. It sounds like a grinding, knocking type sound. The car otherwise drives fine.
Any thoughts from any of you who are experienced with this problem?
The car is a 2000 E46 330D
Thanks
MC
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You could be describing a wheel bearing going out. There is a bearing on the driveshaft that needs attention from time to time, but its speed would be about 3.5 times faster than the wheel speed. I'm going to go out on a limb and suggest a wheel bearing. I would discount the differential itself, mostly because it is swimming in oil and the bearings and gears in there are pretty reliable. The wheel bearings are outboard right next to the tires. One other thing is that the tires themselves can be making noise, but this noise wouldn't change by getting the throttle to sit at just the right place. The throttle will influence the load on the wheel bearings, so this is where I would begin my search.

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