I have a Line 6 Spider II amp that I have owned for a number of years now. And before you start casting down the fact that I own one, listen up. Within the last few months, any time I turn up the amp past 9 o'clock, it makes a high pitched squeal when not playing anything. For those of you who don't know, that position on this amp is not that very loud. I have been using the same presets as I have since I've had the amp, and I have checked to make sure it wasn't the guitar. Any way I can fix this?
Could be a number of things. Have you tried other cables? Are you running any pedals out front?
have you tried turning the amp up without the cable in it? might just be a hardware problem on the amp.