I'm considering buying a peavey xl head on a behringer cab.

The clean channel's great.

However, when I get to the lead channel, if I mess with the master volume, it makes really odd noises, at one specific point it sounds like someone is blowing through a loud microphone. Most of the noises seem to stem from the master volume knob, odd little blips and beeps happen as you turn it, and it seems they can be somewhat tamed by fiddling with distortion and the eq.

My question is, is this a cheap, easy fix, or something (or the beginning of something) bigger and more costly?
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change your cab and the tubes
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