[SECC] Clicks in the loop

[Hoeft, Roger V]

Folks,
 
Anyone have any notion as to what may be the source of  a clicking noise (40 - 50hz) that is picked up by a K9AY loop? The noise is more pronounced on 160M than on 80M.  It's too low in the noise to be heard via the tx antenna, but comes through strong in all 4 directions of the loop.  I'm guessing it's similar to an electric fence / charging device - although I've never experienced one via the radio.
 
Any suggestions on how to locate and nullify the source?  Thanks es will be looking for you on 160M this weekend.
 
73,
 
Roger ...
KA9EKJ