I have a mesa boogie nomad 100 head. On channels 1 and 2 everything is fine, no matter the gain, no matter the volume, but on channel three, if I get it turned up past a certain volume (using the master, the ouput or the gain control) it starts whistling this really loud, really shrill whistle. It only does it on channel 3 and I've even tried standing in different locations and as far away from the amp as possible to rule out feedback and it still does it. It stops doing it when I play the guitar then starts back again when I stop. I've got the amp set to 60 watts its got a brand new matched quad of JJ 6L6 power tubes and 5 brand new JJ ECC 84's and my rig is as currently as follows: Guitar -> New Korg DTR 1000 -> amp -> cab. I'm controlling the channel switching with and Axcess Electronics CFX4 and a Behringer FCB1010. There is nothing in the effects loop. Please help me figure out what this could be. I'm at a loss. EDIT Ok, scratch that. With enough volume, it does it on channels 1 and 2 as well, but they are more like rediculous levels of volume than I will not be using at this point (output on 3:00 master on 3:00). The thing is, the 3rd channel does it at a volume level that I consider relatively low (gain at 11:00, master at 9:00, output at about 10:00). Could it be speakers? It is a small room (10 ft/10 ft'), could it be feedback? I'm really worried here. Please someone help. EDIT II I'm using a Gibson Les Paul Standard w/ Burstbucker Pro pickups.