Mine does the same thing, but it's not the bolts that hold it down, it's something inside. It does not do this when my wife is driving because she has the seat all the way back and leaning back against the firewall. I drive with the seat back up so it makes a popping sound when I take off or make a hard turn.
When I took the seats out, I tried to find the problem but couldn't with the seat out. Hopefully someone else has found it.
