The vibrations definitely makes sense ... When my buddy and I decided to approach a known gopher area on foot with my SR-22, all of them went to ground. Only after waiting 10 mins in a spot that they would shot their heads.
Strangely enough though, we had GREAT luck driving up in my pickup to the area, as they seemed to scurry about without a care for the truck. My buddy acting as spotter, each time we saw one while in the truck, it would act oblivious if we left the engine running, got out of the vehicle, loaded our firearms, then took the shot vs turning the engine off, getting out, loading, then shooting. By time we performed the latter, the bugger was already down his hole.
I've heard from multiple sources to do similar (keep the engine running) if you spot a grouse. On logging roads, they are so used to the trucks going by, that they don't think twice if the engine is running. It's when the engine stops that they start to become spooked.