It sounds like an aftermarket head unit. As such it might need an auto electrican or radio company to take a look.
Definitely would recommend a rolling road run to see. But stage 2 should have upgraded induction kit/panel filter, straight through exhaust, remap. Could be an upgraded intercooler from the sounds of it, any pics?
Should definitely not be loose and rear bench just clips in I believe.
Speak to autologics as various members have used them for retrofits and been happy with results.