Topband: Noise ID

[Tree]

Anyone think they know what this might be?  I think this noise has been 
around for years - but it sure comes up "out of the other noise" with my
new JA Beverage.  I have found the general area it is coming from - about
1.5 miles away to the Northwest.  It seems to always be on - day and night.

Most likely is an electric fence, but I have never heard one sound like
this.

http://www.kkn.net/~tree/NWNoise.wav

Seems to have a period close to 2 seconds - one second on, one second off.
It also sounds like it is a soft turn on/off.  I will try to get a more 
noise free recording once I figure out how to record stuff from the car's
AM radio.

Thanks for any help - perhaps someone has heard the same thing before.

Tree N6TR
tree at kkn.net