dear tony,
when you say that hard vibrations trigger your PCS symptoms, I believe what you are really experiencing is the after-effects of a vestibular concussion or fixed vestibular system malfunction due to closed head injury. your vestibular system controls your balance and equilibrium. It is easy to damage and doesnt always heal up in the aftermath of head injury. you should obtain an ENG ( test of vestibular system) and consider vestibular rehabilitation. Brief vestibular-sensory mismatches could easily disrupy attention and concentration, etc.
leepomd, dr of neurology