I bought a Spider IV 75 last Christmas, and it's worked perfectly since. But yesterday I noticed a weird problem with the nob that controls 'Gain' 'Auto' and 'Pitch'. They sound different and weird first off. The 'Gain' setting makes the volume sound ''drowned'' should I say, and sometimes makes some popping noises. The 'Auto' setting sounds like static and the 'wah' noise is barely noticeable. Lastly, the 'Pitch' setting sounds like a heavy amount of bass has been added and sounds like something you'd hear in a halloween/horror movie. I dunno what's caused this, whether it's a faulty jack lead, or a problem with the amp. But I'd rather have answers before I do anything, because I know next to nothing about amps.

Thanks.