Total posts : 45366
If the interference was just due to the second harmonic then the audio would sound normal. The buzz could be coming from the station’s signal mixing in a nonlinearity in the power lines or system (as Rich mentioned) and that would account for the buzz. If this is the case, the station could be doing nothing out of specification and probably has no control over this.
There once was a complaint from a neighbor who heard my ham radio signal via his TV and I traced the problem to a loose and corroded connection at an amplifier mounted on his TV antenna mast. It was an easy fix but often such bad connections are not found, especially if they are in the power grid.