Topband: RFI question

[Jon Zaimes AA1K]

I have a new, loud noise on Top Band.

It is a buzz -- S9 on some of my Beverages -- and so far seems to be 
here for an hour or two, starting around sundown. I'm not sure if it is 
there around sunrise, and I haven't listened for it in daytime yet.

In AM mode the noise sounds like a steady buzz, and it cycles on/off at 
a regular rate -- 55 seconds on, 55 seconds off. Or at least that was 
the interval tonight when I thought to time it. On previous nights I 
observed the noise started at a lower strength and gradually built up, 
then dropped off sharply when it quit.

I was thinking perhaps a street light might be the source, but canvassed 
the nearby area tonight and found none going on/off. There is a new 
development next door but with only one model house and 3 street lights 
so far, and none of those lights were going off. I did see one 
low-voltage light flickering in a string of several along a neighbor's 
driveway, but the flickering was steady -- the light never went out.

My mobile rig is "between cars" right now but when I get it installed 
again I will try some further tracking.

But any ideas on a possible source would be appreciated. The regular 
rate of on/off cycling has me puzzled -- nothing I've come across before.

73/Jon AA1K