I looked at reviews for the ART SLA-1 and there were inconsistent complaints or mentions about fan noise - some said hardly noticeable and others said too loud. Not sure what to do with that info.
Sometimes one must consider the source for reviews - not always what they appear to be.
I have a ART SLA-1 sitting here beside me in my studio rack which is a 3-way setup driving the HF section of near field studio monitors.
ART SLA-2 in a 3-Way rack for portable PA jobs.
Both are great amps and quiet. I've never heard the fan in either rack. The studio rack is connected to 3 computers with a Crown XTi 1002 driving the subwoofer. After some loud listening or gaming the fan in the XTi 1002 is audible for a few minutes until the amp cools down, SLA-1 is quiet.