In most cases, when components are all using the 3 prong cords, each component in the system has its own ground. Unless all of these grounds are routed back in the electrical system through one point, you get can a ground loop. This is because the components are also grounded by way of the ICs through the other components' ground as well.
If you are going to lift the ground (cheater plugs) try to do that on the preamp and let everything ground through the amps. This is how I get my amp and preamp to play nicely, but my pre has a switch for doing this. I do run a cheater on the QSC amp that runs my bass horns to eliminate a ground issue there.
If you haven't already, try to plug both amps into the same outlet and see if the hum is diminished. Matter of fact, you may need to plug everything in your system into one outlet to see if this helps even more. Use extension cords and/or power strips to get everything plugged into the same outlet and see what happens.
Interesting that you also have one side worse than the other. Try swapping the ICs between amps and see if the hum follows the change. It happens. Just last week I helped a customer with what turned out to be a bad IC, but in this case it was causing the input protection fuses to blow on his amp. Now that's a bad cable!
When you can, try turning off all of the breakers in the house except the one feeding your system and see what happens. This may tell you if the problem is coming in from outside.
Good luck! YOu have my sympathies. I don't think anything is as frustrating as finding solutions to ground issues.
If you are going to lift the ground (cheater plugs) try to do that on the preamp and let everything ground through the amps. This is how I get my amp and preamp to play nicely, but my pre has a switch for doing this. I do run a cheater on the QSC amp that runs my bass horns to eliminate a ground issue there.
If you haven't already, try to plug both amps into the same outlet and see if the hum is diminished. Matter of fact, you may need to plug everything in your system into one outlet to see if this helps even more. Use extension cords and/or power strips to get everything plugged into the same outlet and see what happens.
Interesting that you also have one side worse than the other. Try swapping the ICs between amps and see if the hum follows the change. It happens. Just last week I helped a customer with what turned out to be a bad IC, but in this case it was causing the input protection fuses to blow on his amp. Now that's a bad cable!
When you can, try turning off all of the breakers in the house except the one feeding your system and see what happens. This may tell you if the problem is coming in from outside.
Good luck! YOu have my sympathies. I don't think anything is as frustrating as finding solutions to ground issues.