Have an alpine head unit, using USB, no CD player. Stock bose system. was working fine before. Just got car back. Had engine out and color change.

When the car's still, idling, the music plays normally. Soon as the car's moving, the music skips like a scratched CD. resumes to normal at stop light. head unit appears to be working properly ie no flickering display illumination etc.

The amp was removed but wires appear properly connected. amp bracket is held in by 2 bolts bottom side and a slide in hook topside. easy to wiggle. and pull off and could see this vibrating around when the cars moving. Should the top bracket be tightly held down or is this normal? any other areas I can check. thank you.