Start at the amp and work your way to the front.
With everything off pull the rca's from the amp, then turn it all back on and see if the noise is still there, if not then the problem is further up. If the problem is there with the rca's out of the amp then the problem is at the amp.(ground, ect.)
If you have no noise then put the rca's back in the amp with everything off. Then pull the rca's from the hu with everything off, then turn it all on and see if you have the noise. If no noise then the problem is at the hu. If you have the noise the problem is with the rca's.
Try this and report back