[old_tv_nut]

What Tom said^^^.

If the buzz is really caused by whites being illegally high, it is "overmodulation."
BUT: it could be overmodulation in the source (unlikely) or overmodulation in the receiver itself due to IF alignment putting the video carrier more than 50% down from the high frequencies at the audio takeoff point.

Due to use of negative video modulation, the whites produce the minimum amplitude of the carrier wave. In intercarrier sound detection/reception, this also instantaneously produces the minimum level of 4.5 MHz intercarrier signal.