Adding a wire going from the pot to IG worked! No more hum or buzz when touching the RK27 pot! Thanks again cfcubed!
I think I still heard a very very low buzz/hum with a few tubes though. It wasn't noticeable at all with other tubes. Tube heater voltage didn't matter. Some 12v had the buzz, others didn't. The 6v tube I tried out today was silent as well. Must be the particular tube then. Time to test all 15 or so tubes.