I voided the warranty on the Behringer iNuke 1000DSP last night. I've only owned it a week but that's not a record...
The Behringer has four transistors and an 85mm fan. The fan and transistors are covered by a plastic cowling that is apparently intended to direct the airflow from the fan right over the transistors instead of blowing all over the inside of the chassis cooling things that don't need cooling.
The fan that ships in this amp is L.O.U.D. In all fairness, the amp isn't designed for in-room home theatre use so I'm not sore about it being so annoying. I replaced the stock fan with a much better fan that is designed to run quieter. Fancy blades, motor, and such. "Designed in Austria".
The fan I installed is the Noctua NF-R8 which is slower but FAR quieter.
Because the fan is slower I supplemented the cooling scheme by installing self-adhesive copper heat sinks directly to the transistors. I then reinstalled the plastic cowling to maintain the airflow. I had read that this cowling was the primary source of the turbulence and, thus, noise but I didn't find this to be the case with my slow Noctua fan.
The end result is a nearly silent amplifier. I ran it for a few hours last night while I was painting and it performed flawlessly.