[600MRG] Noise on 600M

[Merv Schweigert]

Several times since I have started to listen on 475 I have
heard a strange noise on the band,  well its not a noise
but a signal.
it sounds like a buzz and will come from up frequency
move down freq,  not sure how far and then return going
up the band at the same speed.
Hard to describe,  sounds like on HF when you hear ionosphere
sounders on 10 meters etc.  only instead of a tone or warble
like those, this is a buzz.
I only hear it before sunset,  as soon as sunset comes or very close
to it ,  it disappears.
I only have heard it 3 or 4 times in several months.  Heard it again
tonite.
I can see it on the panadapter,  moveds across the screen back
and forth one time and then perhaps a couple minutes later
does the same again.
Cannot be here in my qth as nothing changes here day to day,
and I have no close neighbors,  all utilities are underground.
Anyone encounter a moving signal thats a buzz crossing 475
from time to time?
73 Merv K9FD/kh6  WH2XCR