Just tried two different PWM controllers that were on amazon, both by RioRand. One had a reverse option, the other did not. The one with the reverse option made a ton of high freq/high pitch noise at low speeds. The non-reverse model made a grinding sound in the fan motor at low speeds. So both are on their way back to amazon, I have a 50ohm 25 watt rheostat on order I will try next.
Video of the reversing pwm model I tired.https://youtu.be/PCuJ_Mj9-lQ