[RFI] any ideas on this one?

[Roger D Johnson]

Several folks have asked for an audio file of this noise. I don't
hear anything distinctive about it...it just sounds like a buzz.

Looking at the audio spectrum from the receiver is interesting.
There are two almost equal amplitude peaks...one at 120 Hz and
another at 240 Hz. There is another at about half that amplitude
at 600 Hz.

I talked to the cable guys and their amps are powered by 60 volts
AC down the cable. Several amps I saw on the web had switching
power supplies to supply the DC for the amps.

73, Roger