Well that was strange....
Drove home from work, 45 minute drive, drop off coworker, park car on a slight incline (rh side of car low), go inside with him for 30 minutes, and when i leave, the car starts but runs like on 5 cylinders, with an exceptionally loud valve tick. Exceptionally loud!
Shut it down, start it again, same thing, rough on 5 cylinders, loud valve or lifter tick. This time, i give it some gas, and it clears right up, and continues to run smooth as always.
Drive home, no problems.
Go to investigate, and find oil low. 1 qt brings it to 75% full.
Could a hydraulic lifter have ran out of oil due to the low oil level and incline i was at? The BMW cylinder head design apparently leaves much to be desired when it comes to oiling the lifters.
My car is an '06 330i with 111000 miles, so no warranty cylinder head replacement for me.
Filled up the oil, shut down and started a bunch of times, drove around time, spirited and normal, and no further problems noted.