I've got an older Markbass LM III running through an f112 built buy Mark Robertson in Nashville. I get a really loud high frequency hiss even when nothing is plugged in to the amp. It's really noticable when the master is past about 10:00-10:30. It's doesn't bother me too much, just a little anoying between songs and at quieter practices. I'm thinking it could be the amp. It's old and abused, been repaired once (new gain pot after I dropped it). But, it's the only functional amp I have. Has anyone else experienced this with these cabs and different amps? Full signal path: ancient King Mortone->fishman full circle-> platinum pro eq->LM3-> f112 Aside from the hiss, I'm really happy with the sound of this rig for the music I play.