There are filters that can be attached. Look up AC inline noise filters. You may want to try a serious electronics store for a filter or someone like Newark Electronics. Maybe even Grainger or McMaster Carr although less likely.
There are inline filters that place small capacitors and inductors [small coils] across the two ac lines which will kill/reduce powerline carried noise.
Radio Shack , that I've seen, is no longer a good electronics parts supplier.
The problem may be the motor on the treadmill itself. Likely it is a brush type motor or universal type. They can often be noisy. It's the brushes and the arcing, even though minor, which radiates radio interference directly rather than through the AC lines.
An inline filter will not be able to get rid of directly radiated noise but will still kill the line noise.
The ferrite choke may help though if you get a couple more and install one on each piece of equipment rather than moving one around. It may not help but may be worth the try for the $. On the tv I would think the ferrite should be as close to the tv as possible, same on the treadmill. Otherwise the cable may still be picking up the radiation.
You might also carefully check out the grounding between the motor and treadmill frame, the treadmill frame and the grounding [green] wire to the wall plug. Poor grounds can fail to suppress rfi that otherwise would have been reduced.
Your air conditioning motor will be a different type of motor and is likely buried in metal more so the much lower rate of noise generation is killed better.
And of course I could be all wet.
