This is what I was originally thinking but I thought that the receiver always puts voltage out in each receiver slot on the + and - pins, and with only a two wire fan there is no signal to switch it on and off without some controller.

Great Find! Thx! Might try that.

That's correct, the +/- pins on the receiver are all wired together so every set is getting whatever voltage is being used to run the receiver. The signal pin is PWM - pulse wave modulation, which won't work as a simple switch. You need an external device like the one above or these I found on Amazon:

Just a thought, but if you are able to pull the fan wheel off of the fan and balance it, it will probably quiet down a little. May not be doable with all fans, though.

These things are just brushed DC computer fans. I have not tried yet, but I bet we can find better fans from a non-RC vendor... probably cheaper, too. Just make sure not to get a brushless one.