[motomiata]

A late update on this: I have isolated the noise to be on the right hand bank and it is clearly felt on the rods connection the butterflies, as a blow with a small hammer.

My first impression was that it could be a dropped washer or nut bouncing on an inlet valve and randomly hitting the butterfly. I thorough investigation with a bore-scope did not reveal any foreign objects or sign thereof (scratches or the like).

Could it be a misfire blowing back the inlet hitting the butterfly wit a snappy sound?

Any suggestions how to proceed for eliminating a possible misfire?

Thanks