"But when it comes to solid-state electronics -- like an amp or receiver -- I do not understand how typical vibrations can affect the sound."

PMB, it all goes back to the doppler effect-- vibrations in solid state electronics (especially the amp) can create concentrated waves of electrons (followed by a period of electron sparseness), creating an uneven siren-like effect when these bursts hit the speakers. It's like shaking and squeezing a ketchup bottle at the same time!