Sorry about the vague title. so, I have the Hartke HA2000. it's a decent amp for the price. I'm playing a Brice 6 string and it's running through a Hartke 4x10 cab. (None of this is mine (except the bass), borrowing a friend's, who is also in my band) so we did a show a few weeks ago, and a bassist from another band desperately needed a head. I let him use mine, because twice now, I've had to use other people's. Why not pay it forward. well, come to find out, he hooked it up to 2, 4 ohm drivers, and since that set, it hasn't worked. It turns on, light comes on. if I turn up just the volume a humming comes out of the 4x10's that increases in volume, with the volume knob, with or without the bass plugged in. none of the other pots have any affect on any sound/hum. the fuses are fine, and this is the only problem it's had since the owner and I have been using it. (Years now) can someone be so kind as to help walk me through and troubleshoot what's wrong with it. I'd rather not take it to a tech because I can get another used one for about $130. but I'm into fixing my own electronics, and this is kind of over my head.