Do you have DYNAMATT on the inside of the cans.
Dynamatt has a metal top sheet above a rubber matt. Your speaker wires can be grounding out on the Dynamatt and when you attach the cans to the tower you can get a ground or short. This happend to me. I didnt know why my tower sounded funny? till I had wet hands and touched my cans and got a good shock. The speaker leeds that cam threw the cans were ground out on the metal dynamatt
lesson learned