No idea whether it's due to vibration, but the 365C Start and Shut Down procedures don't allow any running at "ground idle". After start, the FFC lever should be "pushed forwards slowly until it contacts the forward stop", and for shut down "Set the FFC in the shut down (fully rearward) position without pausing in the 'idling' detent".
According to my old Flight Manual, anyway: it may have changed!