Installing beat in the trunk aka subs
I need some help on how to get the trunk to rattle with my music
You just need help altogether.
that level of detail simply doesn't exist in the game. The only way you'd get a trunk to rattle is if you were to rebuild the model to separate the trunk from the existing hinge bone, and create a new one to make it rattle. You'd need to write a script to have it rattle on that bone specifically when your music is on, and this would need to be done for every individual vehicle that you want this to affect.
TL;DR you need 3D modelling, scripting and porting experience to stand a chance of making this work. It would take days of work for what is ultimately a very small, un-noticable detail.