8 out of 11 birds over the NE right now are tankers. And they're staying busy.
All the planes they're fueling are not squawking.
That tone is actually pretty tight to 8994kHz…you're picking it up because the receiver is set to the upper side band (USB) as it should be. Tighten the filter as shown in my cap. Turn on the squelch.
You'll notice the signal is there, but I'm not having to endure it.
It's likely a very close piece of electronics to the antenna and it's leaking RF each time it's circuitry is energized.
http://websdr.ewi.utwente.nl:8901/