The original rivet from the Moster185 airbox from Vittorazi, is aluminium and is not up to handling this level of vibration.
Pleace replace your aluminium rivet by a stainless steel rivet (Inox. 5 x 12).
(Steel rivet, with a stainless steel rivet-washer (Ø 5) inside the airbox).
The next units will of course come with the stainless steel rivet.