Joe, I didn't really want to fully take apart the controller since I had the same result with two different ones. I did open it up to check for any burned areas. I carefully ran it with the back off to see if there was any sparking and there was not. I took a couple days away from it to ask around and research.
The information I got was that in these type foot controllers when they haven't been used and have been kept in a damp environment, the carbon will absorb moisture. When the controller is used it heats up and hisses and pops. Once the foot controller has been used a bit it will dry out and the noise stops.
This rang pretty true for me so I gave it a try. I had already noticed that at higher speeds it took longer for the popping to start and that would be because less resistance at higher speeds would build less heat. I ran the motor a few times over a couple hours and the popping reduced very quickly and is gone now.
Yay! Another problem solved in a string of them.
Todays fun was to figure out how to best mount the motor since the bracket has 3 screw holes. Since the machine didn't come with a belt, that gave me no clues. I tried a few different belts and eventually settled on a shorter one mounting the motor higher than my first choice. I think its right though because using the long adjustable slot I would normally want to use puts the motor off kilter and choosing the lower left oddly shaped hole lines up the belt the nicest.
Now that I have the motor running, I found a new problem. When I run the motor, the light goes off. When the motor stops, the light comes back on! Now what?