Can I add a fan to my receiver?

I have a marantz 4500 receiver and the problem is it gets too hot because it is designed for 6 ohm speakers and my front speakers are 4 ohm so I added 2 ohm registers to each of the front speaker and it helped a little but now I am wondering if I can add 80 mm fan on top of the receiver.
Will the magnetic field of the receiver will effect the sound ?

I added a fan inside one of my cabinets, mounted just behind my amp with the air blowing out of the back of the cabinet. It works great, but I finally quit using it because of the fan noise. And it was the quietest one Rad. Shack sold at the time. So, beware of noise if you go this route.

JD