Are you hearing a the amp clip as well or only the visual LEDs
Well, if it's a friend, probably he didn't know there was a problem. Anyway, it certainly seems to be broken now.
As a long shot, I'd disconnect everything and make sure there's nothing floating around inside the amp (turn it upside down & see if you hear it rattle), clean all the connections and try again (using your most expendable pair of speakers). But you'll probably be asking for your money back.