The buzz is due to it being an intercarrier set. The sound is taken off after the video IF. Also could be an adjustment for the sound detector.
Sounds like the Zenith has a CRT issue or color demodulator issue. Try some new tubes. The Hitachi might have the same problem. Do you have a CRT checker?
Not familiar with the LCG396 but it appears to be a very nice NTSC unit. Here is the manual for it:
https://www.radiomuseum.org/r/leader...r_lcg_396.html