Random volume increase

Hi guys. Just got a grandmeister with tm112 and standard fsm432 mk3. I've set presents within one bank I.e. 1a is clean, 1b crunch 1c lead and 1d ultra.

I'm new to the purist way, is there anything I'm doing wrong that is making each channel swell an additional 60% in volume after about 30 sec to 2 mins of playing the respective channel?

Have a full weekend of different set lists and would love to get this sorted before Thursday night!!!

Any help would be very much appreciated!!!

I've owned this amp for a few months and never expirienced anything like that also I don't think there's any settings on this amp that would make it behave that way does it do it without the pedal conected to it ?

Shouldn't happen. If it behaves that way with your guitar plugged straight in, return it.

I've never experienced that with mine, I think the posts above have it right, it's got issues. I had a friend call me last week, he'd just had one delivered and wanted a run through. It was to my eye an obvious return that had been sent out again. I'm a cynical old fart and I concluded that the retailer only had the duff one so did the deal to get the sale knowing it would bounce and by which time they would have a pristine replacement to send out. The one I mention played quite happily when on standby and got quieter as one switched from 18-36 watts which was quite novel.

Ok thanks for the feedback guys, ive made contact with the retailer. they reckon it could be a valve?