A client in the hills above UCLA used to have his DirecTV signal modulated onto channel 17 and mixed into his antenna signal. He could then get it on every TV. This was in the days of analog-only channels.
He called to say the signal disappeared every night, then was back on in the morning. I couldn't get there right away so I asked him to keep the TVs on to see if it stopped at the same time every night.
After two nights he concluded it died at exactly the same time on both of those days. I asked him if he had anything on a timer.
He found that one of the PAR spotlights that came on at that time of day, lighting up the front garden, made a buzzing noise. He took it out and the problem went away.
Another client's Sony receiver would not change volume when the cable box was on channel fifty-something. You could turn it on and off and select inputs, just not change volume.
A good answer is easier with a clear question giving the make and model of everything. "The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
