[RFI] RFI Digest, Vol 92, Issue 3

[G. White]

Powerline RFI is commonly at 120Hz - if it is being caused by a bad 
connection or arching.... the acrching (and noise) takes place  in each 
"direction" of the a/c wave, so you get it at 60Hz X 2....

Check out Merv Loftless's book on AC RFI...or I am sure someone on the=
reflector will explain it in more detail...This isn't to say it could not be
something totally unrelated to AC RFI....but 120HZ RFI is normal for 
powerline noise.

73 Greg
VA3VFO