[Electronic M]

On the modulator, sound buzz on white is a symptom of video over-modulation. Feed the modulator a mostly white buzzy image then turn the video level control down till the buzz disappears or is minimized while maintaining decent video.

By the 12CA5 'lit up like a Christmas tree' is it orange glow from the heater perhaps being ran hard, is it blue/purple glow from the tube being gassy, or the plate glowing red/orange? The first may be a problem but is not as bad as the latter 2. If gassy get another tube. If red-plating you have a bias issue that should be corrected immediately....If you run a red-plating tube for more than a minute you may permanently damage/ruin the tube. Deal with this first if it is the latter 2 issues.

Lastly you probably have minor audio alignment drift. Get a set of plastic alignment tools set the fine tune somewhere between best picture and best sound (maintain some sound to know if the adjuster is improving it's level or reducing it), and adjust the sound IF for best sound, walk the fine tuning towards best picture and repeat. Note all adjuster settings and how much you change them so you can return them to original if no change occurs or the problem gets worse. Do NOT touch the video IF adjusters (those require lots of calibrated equipment, skill, and practice to adjust correctly).

You may want to look at voltages in the synch separator and horizontal AFC/osc sections too...Can you flop the horizontal out of synch on either end of the sweet spot? If not (assuming the hold control is a pot) you may want to center the pot and adjust the osc transformer to synch with the pot centered, then re-check.