I have Dual XDMAR6720 headunit, I have had a 1100 watt monoblock connected to it and 2 12s for about 6 months. Just recently I decided to put a 4 channel amp in and have noticed extreme engine noise coming through the speakers. For the past 2 days I have tried everything, moving the rca cables, putting copper wire around the rca outputs, and i have even grounded my head unit in 3 different places. I think it's the headunit because the engine noise stops when the rca cables are not plugged in, so it has nothing to do with the power wire, besides, they are on different sides of the car anyway. I also don't want to buy a ground loop isolator, I want to fix the problem, not mask it.
The 4 channel is a boss ce404