It depends which 4QDs you have. Mute used to use NCC-70 which blew up (MOSFETs went bang) if we hit something hard... or self righted a bit too high We used to get about 5-6 events out of them before they had to be returned for repair. Mute is a high vibration environment though

Ive heard that the Pro-120 are much more resistant, but I havent actually used them myself.