Double check your wiring.
Then check all the settings on your head unit.
If its all ok then triple check your wiring.
Check everything, power, ground(make sure it is a nice and clean connection straight onto the chassis).
Check your RCA's are in the right spots eg(front - front, rear - rear)
Check the phase of your speakers, positive to positive and negative to negative.
If this doesn't work, then take it to a professional installer who'll probably find the problem inside a minute.
Hope this helps dude.