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i think its related to that whacky that valvetronic mechanism. at certain engine demands the angle of impact between the elements changes quite a bit by design, hence changing the valve lift. it does not seem to be just rpm dependent but rpm and throttle demand dependent.

i had bmw oil in it for most of its life, then i changed to mobil 0-40 and the tick was gone for the first 1000 miles of that interval then it returned. so it seems that viscosity does play a role in this problem. i'm changing to mobil 5-50 next time and see what that does. if that does not fix it then i'll go back to 0-40 and just keep driving it. mine only ticks when cold, after a few miles of driving its totally quiet.