I have a 2008 X5 3.0 and have a tapping noise coming from the engine when I start it up sometimes. This noise does not happen every time I start it up. I have brought my car to the dealership 4 times for this same problem and also sent BMW headquarters a letter giving them a final opportunity to fix the problem before the 4th attempt. The first time they flushed the fluids in the engine. Second time they changed a valve. Third time they didn't hear the noise so they didn't do anything and the 4th time they changed 1 cylinder head. Since this would be the 5th time with this same problem would my x5 be considered a lemon at this point entitling me to either a new car or a refund? Anyone have any experience on this subject and what I should do at this point? I have not contacted the dealership yet.

Thanks