I don't know if this has been posted already of the various sounds of wireless devices:

https://slt.co/Education/EMFSounds.aspx

I couldn't pinpoint the one that sounds like what your meter is picking up.  My daughter has Centurylink Internet and Prism TV using CL's modem set to a wireless broadcast.  I was actually OK with it on while I stayed with her.  I have an HF35C and the wireless signal was very low powered.  She moved and Centurylink gave her a new modem and she says that the signal was so powerful that she could feel it so she called CL and they were able to turn it back down..