My car hows 2 kicker 10's, a new touch screen double din radio, and a flowmaster axle back exhaust.

problem just started, on defrost all the time now.
my mustang is a v-6

rear squeak when causing in my mustang its a 2009 with 50k miles..great condition bought CPO. anyway recently when going 20-50 i hear a squeak from the rear of the car..but it goes away when i hit the brakes or accelerate..only when i cruise and don't touch the break or gas it squeaks. Please help

how much to replace the front bumper and a headlight cover-was in an accident