cheers for the suggestions gents! No I don't use heavy acceleration on a cold engine, I'd say engine oil is about 40 degrees and it's between 3-4k rpm. CV joint could be possible, but then I don't hear anything with a warm engine. I do have a persistent CEL for one of the O2 sensors, maybe the mixture is off a bit sometimes, because swapping the sensors didn't make a difference, camshaft position (1 out of 4) sensor also gives a code.