The first question that I have is this: is the seatpost carbon or aluminum? If it it carbon, make sure that it has some carbon "grease/paste" on it. This works well for carbon and doesn't allow it to move.

AS others have mentioned, with larger tubing in frames sounds often travel through the frame making it difficult to isolate where the sound is coming from. Check the obvious: seat, bottom bracket and bolts on his chainrings, crank bolts.

Good luck and definitely keep us posted!


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