CTC-16 Issue

[jstout66]

I have an odd issue on my CTC-16, and I don't have a lot of test equipment anymore, but maybe I can figure it out with your help, or pass the info on to a TV tech friend here in Omaha.
After the set is on for about 5 minutes, I start hearing a whine. (like high-voltage or oscillator) when it does this, I don't lose complete focus, but it's like it's razor sharp on the top half of the screen, and slightly out of focus on the bottom half. Horizontal hold and color remain good. I just put in a new 6JE6, and no change. Are there any other tubes I should change in that section, or does it sound like something else?