I get the high pitch shrill when I am plugged and the volume is turned up all the way on the guitar regardless of which one of my guitars I plug in, my Les Paul Classic, SG Special (P-90's) Strat and Esquire . If I unplug my guitar and the cable stays in the input jack it makes the high shrill sound also. I tried a half dozen different guitar cables too. It does NOT make the noise when there is not a cable plugged into the input jack.
It just started making this noise when I turned it on to play some this weekend. :(
