I think my Dunlop GCB-95 is screwed, all it does it make a really high pitched squeak when it's in the treble position. Is there anything I can do to fix it? I've tried a battery from one of my other pedals, and it doesn't help. The battery is still pretty new...

By the way, it's pretty old judging by the looks it
are you sure thats not feedback? if you're using high gain settings, and/or too close/facing the amp, that's bound to happen.
Live Rig January 2018

Fender Baja Telecaster/Danelectro DC-12
Boss TU-3, Ibanez TS-9, Fulltone OCD 1.7, EHX Small Clone, MXR Carbon Copy, EHX Holy Grail Neo
1964 Vox AC30TB with '69 Rola G12M "blackbacks"
Elixir Nanoweb 10-52 strings, Dunlop Jazz III XL picks
apparently they squeal real bad if you have the input and output leads mixed up
Get off this damn forum and play your damn guitar.
It squeals because it does not get enough power, try a fresh battery and/or a 9 volt cable and make sure all the wires are ok...
check if its hooked up right, if not change batteries. if that doesnt help, come back here