Remote from the head unit
If it were me, I'd isolate the three common wires one at a time to see if you can make the noise go away. I'd first run a jump wire from the battery to the amp triggers. If the noise goes away, then you know it is in the head unit- probably a dash ground.
If not, try a jump wire on the amp ground, and finally a power jump wire.
like "Bob" said, there are limited things that can be causing amps to make noise.