Already you have provided a relevant fact that was not provided previously. A tiny example of what you must provide to have answers. Suggested was how to provide relevant information. Why is this simple request so difficult?
Why is that important? You don’t know why. Which means it is probably so important that you consider sacrificing the dog if necessary to answer it. Facetious? Of course. But decades of complex engineering is the easy part. Clearly the most difficult part is getting answers to relevant questions.
You are trying to understand only what you already know. That means you read something only once and know. But anything you don’t know means rereading multiple times. That is what I always have to do. If something is new, I never understand it in the first read - never. If anything is important (and unknown), then multiple rereads are probably required. If not, then you will only have headaches - and learn nothing.
Well, one likely problem involves a gain problem inside the switch. Also called signal to noise ratio. But we cannot discuss that due to virtually no facts. This much is obvious - without doubt. AC hot wire is definitively not related to your problem. Move on to the other suspects. Again because these sentences summarize everything:
You provide the facts. The internet then used knowledge you do not yet have to suggest solutions. But no solutions are possible because you do not provide simplest facts.
Unstated was how video enters. Is it coax cable? Is it FIOS? Nobody can see this stuff. Without critically important facts, then every answer will only be wild speculation.
ZenBeam - for high frequency noise to enter on AC mains, a switch’s supply must be so defective that the switch is defective. Do you understand what a power supply does? How does noise get through all this?
First it has a massive filter well beyond what that X-10 filter does. Then it converts AC (and low voltage, high frequency noise) to high voltage DC (more than 300 volts). That high DC voltage is further filtered. How many filters can that noise get through? And somehow an X-10 filter designed do something else will eliminate that noise?
Then the supply converts that high voltage DC to high voltage radios waves. Then filters and changes that high voltage to low voltage. Then converts that radio wave to DC. How does noise not get converted to pure DC? Then another filter. How many filters is that? Each filter superior to what the X-10 filter does. How does your noise withstand multiple AC to DC conversions - and miraculously blow through? Did you even know how many filters are already inside that switch?
Noise may bypass all that - with or without an X-10 filter. Therefore a relevant question: which boxes are using three prong and two prong plugs? And how are these boxes interconnected?