I've got an old beater Sundown SAE-1000D that's close to a decade old now, and it's having an issue where the output will go from normal to about 30% or less at random. Power isn't an issue, my 4 channel and sub amp share a 0awg feed and ground, the issue happens at all volume levels, and I don't have issues with the 4 channel amp. Connections are all nice and secure. When the output volume drops low, if I crank the volume or turn the sub level up, it'll come back to normal like flipping a switch. There's no bass knob hooked up. I'm leaning toward faulty inputs on the amp, or bad RCAs because I made a turn today and during the turn, the output was right where it should have been. Any ideas what else I can look at?