On 7690 kHz, I came across a strong signal with a constant humming sound. If I tune up or down 5 kHz, it's not audible anymore, leading me to believe that this some kind of broadcast. The tone reminds me of the sound of a small prop plane flying overhead, but at a constant pitch. There's volume fluctuation, but I can't tell whether or not it's due to fading.
EiBi doesn't list anything for this frequency, and it isn't in a broadcast or ham band. Unfortunately, I'm getting a lot of noise, so I can't make a decent recording. Any ideas what this could be?
(Eton E5 + indoor wire antenna, northern California)