Emiliocharvel

Hello I bought my spider IV 75 about a year ago. In the past few days I was playing during a reahearsal and I started to notice like a "saturated dirty" sound coming out from it. Specially when playing it loud and stomping over the A function switch of my shortboard for the extra boost. The sound starts clean and then it kind of ripps. Like if the speaker was blown. If I turned it down and turn it on again the problem goes away, but after a short it comes back again. I lowered the Master knob a little bit and it dissappears. If I raise the Master knob again just a little, the problem shows up again. I noticed that the amp is real hot when I touched it last night. Does anyone has a clue of what might be the problem. Thanks.