shot in the dark
I'm not a big tech guy, but some thoughts:
No hum thru the HDMI is probably because it is digital and not picking up RF interferance.
Other hum is probably an RF being picked up, like an antenna, since that is all analog connectivity. You could try different ground points. In audio systems hum is always a ground problem. Is the RF module groundable? Not sure what RJ6 is.
If the hum sounds moderately low in pitch and constant its probably a 60 Hz feed and the tv may need grounding. If its different, then the wire acting as an antenna is more likely.
Hopefully a smarter guy than me will answer.
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John and Caren, Arkansas. 2006 Newmar Cypress 5th wheel. "Fractured Fairy tails"
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