What operating mode/emission is this

N4AB

I keep running across this Signal(???) that appears to pop up on a single frequency then evolve into multiple tones that spread across the spectrum. Just before the signal stops, it starts to collapse back into the single frequency it started with. (but the signal stops before it gets back to the original frequency). Has this question been asked and does anyone know what the answer is?  

Ria

It almost looks like a birdie from some piece of equipment nearby.

N8AUM

How much time between when it starts to when it stops and does it start over again? Slow down the display rate?

FISHULA X

 I get the same signals from my LED TV,. Although, you can't hear the signals, I can see them when I turn on the TV and goes away when it's off. This only happens once in a while depending on what channel the TV is on.. This is what it looks like to me on your waterfall.  Keeping in mind that the Flex is very sensitive to picking up any local signal traces that may be coming to your radio locally. Sometimes it's there for a while then disappears after a while. It could even be a Led light bulb. I also notice that if I click on the WNB it usually takes it away.  

Cal N3CAL

Most likely a HVAC system electric motor turning on. 

Pat Hamp

Spread spectrum, based o n a modulated signal.

Pat

John - AI4FR

Cal beat me to it. That looks near identical to what I see when my HVAC turns on. Normally only seen on 15, 12, and 10m.

Ken - NM9P

That looks like the “fan” pattern generated by many variable speed motors on HVAC equipment. Or it could be generated by one of the new front load washing machines. I used to see it a lot on 160 Meters. I’m surprised you get it all the way up to 15 Meters! Perhaps my HVAC was a little older than some of the new ones....