Peavey Vyper 75 watt amp making a wah noise when playing chords?

I know there is a "wah" setting on the amp, but its not on. I'm sure of it. i have it on K-stein with stompbox and effects both on bypass. Every time i go to play a power chord and hold out the chords, the sound begins to go up and down kind of like the wah effect. this only happens when i play power chords. just playing a single note and holding it, it sounds fine. or if i have it on a clean setting it sounds fine as well. I'm not sure if its the amp or my guitar. i have a ibanez rg5ex1. i was told the pickups on this model weren't very good.. Any suggestions on what the problem may be? its really getting annoying