Well from experience in hooking up litterally hundreds of sytems over years, I can get rid of pretty much any hum from tinkering a bit I suppose. Usually you should first try using a cheeter plug on one of your 3 prong plugs, either on the preamp or amp first.(they'll all still be grounded through connection to one another). Usually, this solves the problem of blatent hum off the bat. Sometimes interconnects or speaker wires are running next to power cords too closely for stretch, and can have hum in the wires that way, but usually not. I have run speaker wires next to high voltage cables with loud buzzing and humming, that's to be considered.
I once hooked up a really really long pair of Interconnects down 2 sides of the room, running along the same path in a wall with some power cords, and it buzzed like crazy.
Anway, hope that gives some food for thought. But I think you might try the ground cheater plug thing first. That usually works. Then, you can try moving your interconnects around, while your system is playing, and see if it's a problem. You might find that if you get the interconnects to lay in a certain way, you'll virtually eliminate hum sometimes.
Good luck