I thought after all the work I put in on my 2000 one I could manage to figure out easily problems on the 20004 one, well... it doesn't seem to be the case.

So, I have a weird noise that comes on sometimes under acceleration around 20-30 km/h. The noise sounds like a loose plate or main pulley/pulleys, like something that's not tighten. For example if you take the belt out of a dumper pulley or water pump and if these are not tight enough, being wobbly they will touch the engine cover or something like that when spinning. That's the kind of noise I am hearing.

The other problem is that I cannot pin point to it when I drive. Sometimes I swear it's from the back of the engine and sometimes I hear it underneath the car where the transmission is or a bit to the back towards the transfer case is or rear driveshaft.

Now, when the problem happens I get a bit a lower power than usual. The wobbling plate/pulley/clutch/drum... whatever is loose there is not letting to spin free and it sucks some power.

I don't hear it at higher speeds but it might be because the road noise and again, it is not happening al the time either. Warm or cold engine or transmission, the same thing.

I put it in N and rev the engine to figure out if it's engine or tranny and I thought I heard it one time but recently I don't hear it when parked.

Sorry guys, that's all I could come up with for description.

I went under the car and nothing seems loose. It could be in the transmission, or torque converter, or transfer case or where else?
The transmission seems to shift well. I changed the oil in the tranfer case the other day. I filled a 1/2L oil in the transmission as well. I can take the tranny oil pan down and change the filter and see if I can find something in the oil but I wouldn't expect since the shifting is good.

Could be a bearing somewhere? differential bearing? how can I tell?

Anyway... any thoughts where I should start debugging this problem?

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4.8is 2004 imola red
4.8is 2005 Black on Black - DINAN/2 sold
4.4 2004 X5
2003 330xi
2008 328xi - sold
4.4 2000 X5 - sold