I replaced this part and it had no effect on the noise. I previously replaced the a/c and power steering pulleys and it had no effect.

Then two days ago I got a CEL and found a hole in the inner manifold, so had it replaced. The mechanic noticed a bad DISA valve when he was doing the work and replaced it also.

Now the sound is gone -- it was the DISA valve all along!!!

So if your X has a rattle under acceleration, check this valve. Apparently it fails all the time and probably should be replaced routinely at 100k along with the plugs. My car has 150k on the clock.

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Mark
2001 3.0 Original Owner, still going
2012 E70 xDrive 35i Pre-Owned -- sold because no one could figure out the transmission problem