Hi, I have been in possession of this motor controller for a while. I try to control a brushed car radiator fan with it (12v, 10A). However, the fan creates a very whiny noise. I tried lots of different PWM frequencies but to no avail. I am using a Raspberry Pi 3 to send the PWM …

You mention in the subject that the MD10C is noisy, but write that it’s actually the fan? https://www.robotshop.com/en/cytron-13a-5-30v-single-dc-motor-controller.html Try applying full voltage and listening to the sound of the fan (i.e. no PWM). You might try adding capacitor…