[RFI] Rectified 120Hz RFI?

[Andy]

Just thinking, there are many possibilities for what might cause it to
be 120 Hz instead of 60 Hz.

One being something gone wrong in a full wave rectifier.

Jim's suggestion of arcing on both excursions seems likely too.

I suppose it might also have something to do with the zero crossings.
Things like triacs tend to generate RFI because they switch on and off
every half cycle, 120 times a second.

Andy