Thanks for the update.

Since you have the ground-loop isolator on your incoming TV cable, then I'm sure the loop is happening through the AC/DC adaptor to your laptop and the rest of your gear. Running the laptop on the battery with the adaptor disconnected will confirm that if the hum disappears.

Then you can experiment with different AC plugs and your equipment.

Good luck!

Alan Lofft,
Axiom Resident Expert (Retired)