[RFI] Powerline noise humps?

[David Winarsky]

I wrote a couple of months ago for looking assistance in tracking down a noise source, and with the help of the list I located 6 (!) different noisy power lines within a 2 block radius of my house.  I’m currently working with the utility company to address these; they’ve confirmed and fixed 3, while the other sources weren’t active when they investigated (despite the fact the I had video and audio of me locating the source).  Thanks to everyone for their help.

After locating all of the above, I thought I was honing my skills at RFI hunting, however I’ve got one last source that has me stumped:

I’m experiencing what sounds like power line noise on 20 meters, but is in “humps” almost exactly 50 Hz apart.  They are occurring at 14.120, 14.175, 14.225 and so on.  I’ve tried to locate the source with a loop and portable SW, however I’m not able to pick up the signal on foot from the ground (my tribander is at 40 ft).  Has anyone seen powerline noise represent itself with these humps of intensity?  The noise does not drift and an audio spectrum analysis shows a huge peak at 120 hz.

- Here is a capture from my waterfall: http://imgur.com/HyuFcyK

- An AM sound clip centered on the hump: https://clyp.it/imfp5ypl

- And an AM clip tuning across the hump: https://clyp.it/nv4efvyc

Appreciate any ideas on what this might be or how to DF it.

73,
David NY6W