@fredrik222 With regard to racks, have you checked out Salamander?
Modular Open Stands | Pro Audio Racks | Pro Audio Acces - Salamander Designs
I've got one of their Synergy modular racks without any front, side or back panels and this works quite well with my McIntosh integrated. My MAC doesn't have a fan and, frankly, stays quite cool to the touch, even after many hours of duty but MAC recommends good ventilation. Even with a glass front panel, dust will always find a way, if you know what I mean. If you kept it covered when not in use, you could still remove the cover and watch the meters dance around when the music is playing.
Another thought: is your amp positioned in proximity to a back wall? Since the fan exhausts to the rear of the casework, any chance what you're hearing is actually the fan pushing air up against a back wall that is too close and not fan noise itself? The shop I was in when I spent time with this amp had it on a rather tall rack, as I indicated in my initial post, and the wall behind it was probably a good 3' away. Of course, I didn't know it had a fan at the time and, as such, wasn't making a point of listening for that sort of thing. However, I was close enough to this beast and spent more than a few minutes eyeing and coveting it without noticing any fan noise at all. Maybe dust accumulation on the fan? I know this is nitpicking but just trying to help. Bottom line: If ya can't hear it when the music's playing; ain't a problem!
Enjoy! Go play some music!