This is the reason I don't like the Sony Units. I originally had one and not only did the fan make noise, it also bled RF noise into the line out... so the fan noise was amplified! "The reason I tried the sony was that I have AIWA CDC-MP3 units in both of my cars with the line-in feature, so I could move it between cars... but had to give up on that idea and returned the sony units. I was told that the fan noise was a common return.
It's 9 months later, and I just installed a Pioneer Unit (It was offered to me for only $99 including Antenna and Activation!), and it's great! (XM903), using the RF, but I'm considering upgrading to a Pioneer head unit (although sound quality is quite good!) in the future. No noises, and installation was quite easy... but can't move it around like the Sony... I wish Pioneer would make a unit like the Sony. I've always thought of Pioneer being higher qulaity than Sony.