Originally Posted by Graphite Shark
Same issue here as well. Most apparent in a fast food drive-thru while waiting in queue. The engine will drop to a very low idle, then CLAP CLAP CLAP CLAP sound. Giving it even the very smallest amount of throttle will very slightly raise the idle speed and the sound goes away. If left to idle back down, the sound returns in a few seconds at most.
Does not happen all the time, fairly rare, though annoying and very apparent when it happens.
Not the injectors- they make a ticking sound; not the waste gates, famuliar with that rattle in a tin can sound. This sounds like a small hammer hitting the side of the block, or a timing chain slapping something; even slightly like a main bearing.
I know some engines use a timing chain tensioner which uses oil pressure to press a small "shoe" against the side of the chain to keep tension elevated. Not sure if the N54 does as well, or that's a factor.
I just notice mine today and came across this thread. Noticed it at the drive-thru.
I just ordered a cobb and my CPO just expired this month. Sound like the rocker arms or valve tap. I guess I am going to see if BMW will take a look before I install the COBB.