Topband: Need help identifying RFI source

[K4RO Kirk Pickering]

I have been plagued recently by a noise source which is
wiping out signals on the 160m and 80m bands. It is 20dB
louder on my SW Beverage than any other direction.

The noise is intermittent, and comes on for roughly 10-15 
minute intervals, and when it goes off, it is completely 
quiet for another roughly 10 minutes. The amplitude peaks
are at approximately 20-30 kHz intervals, an seem to vary 
somewhat with frequency. I can hear the noise from about
1600 to 4200 khz. It's really hurting my 80 and 160 meter
reception. Here is what the noise sounded like this morning:

http://www.k4ro.net/k4ro/audio/QRN_Jan24_2011.wav

Before I start hunting, I wonder if anyone has heard this
type of noise before, and might be able to identify it? 
Thanks for any suggestions.

73,

Kirk K4RO