Need some help with an amp.

Once again, I need some information/help. I just got an Aragon 2004 from ebay. I am getting some humming/buzzing from the speakers. It is louder from the left speaker than it is from the right.

I disconnected everything, unplugged everything except the amp and the left the speakers connected and I'm still getting a hum. So, I plugged everything back in.

Now, for some observations.

1. Everything was plugged in and connected. My preamp was in standby. The switch on the amp was off. I unplugged the interconnects from the amp, so that amp is sitting there, plugged in with the speakers connected with the switch off and nothing hooked up to it in terms of interconnects. I grabbed an interconnect and got a loud hum from one of the speakers. The only thing that the interconnect was connected to was the preamp (NOT the amp).

2. I went to plug the interconnects back into the amp. The preamp is still in standby and the switch on the amp is off. With one of the interconnect plugs in my hand, I was reaching behind the amp to plug it in, my bare arm touched the amp and I got a little shock. Not a big one, but I can definitely feel a small current.

3. With the preamp in standby and the switch on the amp off and the interconnects disconnected from the amp, I touched my bare arm on the case of the amp and grabbed the connector on the interconnect with my other hand and felt the "shock" on my bare arm.

Can anyone tell me what's up?

Thanks.