[RFI] Pulsing RFI?

[Brad Pioveson W9FX]

Hi, all.  After several years of having little interest in the 80M band, 
today, I strung up an antenna and, was greeted by an odd signal that has 
been apparent at 80 kHz intervals across the band continously today.  The 
peak of the sig appears to be at 3.775 MHz and, they extend well past 4.5 
MHz at that ~ 80 kHz interval.  The pulses are approximately 1/2 second in 
duration and are almost, but, not quite, sync'ed with the second hand of the 
clock.  Occasionally, one pulse will almost be twice as long as the others - 
usually, this happens about once per minute and at random intervals.  I've 
eliminated possible sources in my QTH - including what I perceived to have 
been the logical sources:  digital alarm and VCR clocks, PC's, DSL modems, 
and the like.

This is a new one to me.  Before I drag out the sniffing gear and cobble 
together a rudimentary DF antenna for 3.5 MHz, does anybody have a clue as 
to what I might be hearing?  Does/can digital CATV, which has been installed 
in the neighborhood since my last foray on to this band, ring any bells?

73, Brad, W9FX