Audio "buzz" on a 1948 Motorola VK-101

[old_tv_nut]

Wild guess:

Does the buzz change when you adjust contrast? I wonder if one of the video IF tubes is weak, causing you to set the first video/audio bias (contrast control) to a strange level to get a picture. If you can get non-buzzy sound with the contrast turned down, then maybe tube replacement or swapping around some of the 6AG5's may have an effect.