I recieved my HD500 yesterday through the mail.  Once I got the item, I installed the drivers, updated my firmware and made sure everything was setup right.  Here's the problem: regardless of any cable or guitar combination that I've tried, I'm getting a loud almost electrical buzz from the unit.  A friend and I tried out the same guitars and cables through an HD300 of his, and it runs silently...  this is even through the same power outlet, and combinations of equipment.  I also noticed that it was odd that I got the same buzzing through the USB audio input as well as an issue where the USB cable doesn't seem to make connections quite right.

Any thoughts on this?  I've tried everything I can think of, and I'm starting to question if the unit I recieved might be faulty and need to be exchanged.

(Just to provide you guys with as much info as possible, the buzzing comes out ALL the outputs, including the 1/4" line outs, the XLR outs and the USB output...  I tried switching the ground lift on the XLR to see if it was a ground problem, and it almost sounded worse.)