Intermittently my Spider Iv 150w head will change to a clean sound in the middle of a song when playing distorted tones loud with the whole band. ??? Help. Is it over heating, glitch? Not all the time but when it starts doing it it keeps doing it. Usually I have to put the head on the floor. That works most of the time but it's getting worse. Thanks for any advice. I use this to gig and have a bunch of travel shows coming up.