So I just finished amping my 4 corners and my sub (4 chan + 1 chan) and my 4 chan is buzzing when my key is set to ON. When I'm in ACC, it's perfect, but when I go to ON or actually turn the truck on, I get a gnarly buzz in the system. I haven't installed noise filters yet, and I've inspected my grounds. I'm using 1/0 ground wire on both amps, running about 10" long on each one, grounded to my chassis behind the trim. I cleaned the paint off, and I've already ensured the bolt holding it to the frame is still on tight. I've also upgraded my chassis ground to battery to 1/0 as well, and that is running a clean connection as well. Again, it only does it when the key is in the ON position, not the ACC position.

 

You have power flowing thru ground with Key ON.

Unplug the receiver's audio cables from the amplifiers, see if the noise goes away
You are trying to find out if noise is in amps or receiver