Yeah sorry for not answering, but I really think you have only two options here:
1) Replace the cables (shielded cable for the sensor)
2) Use linear motor controller
The truth is that when you have 25ft of cables close together and two of them are driven by a high-power switching amplifier, you will have serious noise problems.
I could think this further, but you would need to provide more detailed information. What is the sensor and how it is wired (both power and signal wires). How is the motor wired (what kind of cable, what kind of filters). The physical connections and their locations are importan.. maybe even photos of the devices. I also would need to know the model of the pwm-controller and how its power supply is connected.