ok my friend has 2 audiobahn 12's and phoenix gold amp. when the system is off and he is driving the subs will start to boom and they pop when there are bumps in the road. also when the car is turned on and is parked you dan hear the engine idling on the subs. He replaced his ground wire and his power wire to try and fix the problem but it still happens. I was thinking it might be the rca's to the HU what do you guys think.
Sounds like there is a loose connection. Check the power wire, the connectors, fuse holder, ground wire, everything before continueing further.
As far as engine noise is concerned there may be two reasons;
Bad ground connection.
The power wire has been tapped into another power source.
MAKE SURE THAT ALL OF YOUR WIRING ARE SEPARATE FROM ANY OTHER CIRCUITS.
Poping sounds may be because of cheap or bad RCA cables, loose speaker wire connections (inside the box, at the terminals, binding post, or at the amp) ineffective grounding, or voids in the power wiring.
Its all about the wiring.
something exactly like this happened to my b/f. he now drives with the cover off of his kicker amp and has no more problems. there was something wrong with the connection inside. his wires were fine
is the power wire and ground wire run down the same side of the car? this can cause alternator wine. as far as popping that is deff a loose connection I would make sure that if he installed the system when he put his rocker panels back on make sure he didnt knick the power wire and when he hits a bump it might ground out causeing that loud pop. Also check the fuse holder and make sure that a single strand of wire isnt hanging out that might hit the body under the hood and ground it out. There are many things it could bestart at the battery and work your way back.