[RFI] Horrific Ugly Noise, thought I had it!

[Dave Cole]

Hi,

Well, I know what it isn't!  I thought I had a noise pinned down to a
house.  The noise at the house is gone, and the noise at my place
persists...  All of 40 meters is shot.  It is frequency specific
however, starts around 6.5 MHz, and ends around 9.5 MHz, slow build up
and drop as I sweep. Used a BWD-90, broadband antenna to verify it was
not my antenna BW causing the tight frequency range, and a portable SW
radio, it really is between those frequencies... 

I took several measurements of the audio portion as viewed by my
computer on the radio audio output, and I found some very interesting
things...

1.  There is an audio pulse every 720 Hz or 12 times 60.  This makes me
think it is power line related, although I have no idea why 720 Hz...
2.  The noise is on 7 X 24 X 365
3.  It appears to be spark like in nature, see expanded and wide views
of waveform as captured on an O-Scope.  Can someone verify this
assumption please?

Can anyone suggest what this might be?  See:
http://db.tt/eSA0bq4
for images, and a sound cut as an MP3. 

Thank you,
Dave
NK7Z