I'm using a Peavey Minx 110 (a bass amp) for my guitar.

There is a post gain knob. When i turn it it makes a screeching... screech lol. Sometimes pops and feeds back a bit. I have read that its dust... It is an old and unused amp. So if i were to clean it, what would i do?

Open it and dust it out?
Maybe a connection problem?

Anything would be great guys. its really busting my ears over here.