#1
So, I have a Peavey Ultra 112, which I got used, and it was working fine for a while. Then, when I turned on the built-in reverb, it got all staticky and it sounded like it was going through a filter. I tried flipping some of the switches on the back that control how many ohms it uses and GND.(Whatever that stands for) Does anyone know what's wrong? It's a tube amp, if that helps any.
#2
Gnd stands for ground. DO NOT mess with the impedance switch on a tube amp. You can fry the output transformer this way, and they are not cheap.

The static problem could be a dirty or worn pot. Very simple and cheap fix. When the pots (commonly and incorrectly called knobs) get dirty or worn, the sliding contact inside makes intermittent contact with the resistive element and you get static and noise, sometimes even when you aren't even touching it.

That's all I can offer with the info you've given. Hope it helps.