Randy,
You said you have the HT on an independent circuit. Do you know if it shares a neutral with that lighting circuit, or was the wiring home ran to the panel for the HT circuit? If they are sharing a neutral, the circuit path will still be routed through the lighting fixture (neutral to ground) regardless of whether the light switch is open or closed. If any of the fixtures on that circuit are not properly grounded to the ground wire, you could be getting feedback on the neutral. I’m not saying this is your culprit, but it ‘could’ be.
Let me know and I’ll run this scenario by one of the EE’s at work to see if they have any ideas.
