First thing to do is figure out where the hum originates. To do this, you have to switch channels, first on your speaker cables, then working your way up the chain of interconnects. Connect your left-hand cable into your right speaker, and vice versa. If the hum stays on the left, the problem is that speaker. If not, revert the cables and switch the I/Cs between amp and preamp. Again, if the hum stays left, the problem is in the amp (or the left speaker cable, but you said you switched those out already). Keep trying this, and you will at least know what piece is giving you a problem. If you start from the speakers and work backward, the problem will be in the component or wire immediately downstream from whatever wire change DOESN'T cause the hum to shift to the right.
Slight hum from left speaker -- Help appreciated
Two weeks ago I installed a new amp and preamp (Pass Aleph 30/FT Audio LW-1) in my system and since then I've had a very slight hum from my left speaker. It's not distracting, but it's something I'd like to get rid of. I've switched out interconnects and speaker cables and nothing changed. I did a search for ground loop hums and I could not find any useful information other than cable TV may be a problem and we don't have cable. Any hints on what could be causing the hum would be greatly appreciated. Thanks!