HU and woofer installation doesn't void warranty if you do a socket-to-socket job. No wire cutting!
The tire pressure in your tire should be 33psi. Again that's given both in the manual and they must have told you when handing over. If you are putting 40, you are over inflating and the ride will be rough. Even at 33psi, the ride in the rear is rough. I found through trial and error that 31psi is more appropriate in the city. Note that the pump gauges are almost never calibrated, so don't believe it blindly. Check the pressure at another pump just to be sure
Ameyam