it wont fire. Down here in good 'ole Texas you dont need no stinking permit to carry a loaded gun in you vehicle. Now that i think about it i dont think you should anywhere. Its protected under the kindom clause since your vehicle is part of your domain, like a house, so legally you can carry a loaded weapon within it at all times as protection. Just like why you can refuse entry to a police officer who asks to come into your house without a warrant, you can do the same with your vehicle.
As long as your gun has a proper safety, there is no reason it should ever fire from bass vibrations. Ive seen this discussed many times. As for people who have done real world testing in loud vehicles (louder than me), i know JP always carries and handgun on him, i saw him at Turkey drag and he had a pitstol on him walking around, and demo'd full tilt with it on him. Thats 10x18s so that was enough to know it isnt going to happen.
Fidelity--Built To Last--Team Sound Asleep