I haven't had any problems. Had it I guess close to 2 years.
When I first got it, I thought I should be getting more volume, but Ive found d that I was too shy with the gain knob.
Coming from a genz .2 model, I was used to more gain=distortion. The gain in the MM doesn't have this effect. I would have the gain around 10 to 12, and it just wouldn't cut it. Now I use it at 2-3, and no complaints.
Haven't noticed the fan, but I only use it during rehearsal or gigs.
Haven't heard any high pitch sounds from light changes (as an aside, my lights only change when the mute is engaged on the amp.).
No problems cutting out.
I'm using 12/6/1+12sub usually.
No complaints.