If it were all running on DC instead of AC, I would say that any one of the Radio Shack noise filters designed for car audio would work. However, I know nothing about AC.

I had a similar problem in my old Volkswagen. Every time I stepped on the brake pedal, there would be a pop coming out of my amplifiers as the brake lights kicked on. I fixed this by literally putting a noise filter on the wire leading to the switch above the brake pedal under the dash.

I would think that the cooling fan you're using would be noisy when you're watching a movie, though. If it were me, I'd be re-arranging my cabinet to allow for more proper ventialtion (amplifier on the bottom with a 6" space above it) instead of adding a noisy fan.