I don't know if it's the same. I have on 500 kHz an unid signal from TV sets.
It's not only mine but also from the neighbourhood. I always know when they
went to bed ;-) First I thought if came via the AC net, but even when I use
batteries that 500 kHz TV signal is there. Even when I were on a campground
I was able to identify 2-3 TV sets from other campers. I don't know what
exactly is responsible (inside the TV set system), but it came 100% from them.
Maybe that is also your "problem" ?
73, Tom - DL8AAM