Originally Posted By: bmwtechguy
Sounds like a hydraulic lash adjuster that is not pumping up, possibly due to small piece of trash trying to circulate through the lifter and to the oil filter.
That's an interesting diagnosis with some possible merit IMO. I have not had this problem (yet) on my AP2. I am aware of many AP1 owners that have experienced it though. They have found that by replacing the TCT, the noise goes away. But for some, the noise returns after 10K miles or so. There is some speculation that a worm gear is getting worn out and modifications are ensuing. There is also speculation that M1 is causing the problem (probably just anecdotal though). Anyways, I've been lucky so far, I guess.