Sounds like someone's broadcast ssid on a wireless network nearby. See if you can connect to it, then figure out who it is.
Tell them about security, and the fact that anyone can surf into his network as long as he is broadcasting ssid ( a small white lie😉 )
get him to turn off the ssid broadcast that way😀
There is no other way to get rid of it, if it is a nearby wireless. It will always show up.