I get this a lot as well. Especially seeing shadows move and things in the corner of my eye.
I also hear things. Voices in water and people yelling my name along crowded streets. It's very unnerving.
I don't hear beeps but I do get tinnitus I think, ringing sometimes in my ear or music playing without any stimuli.
I'm not sure what it is either. I used to think, and sort of still do, that it was things from another dimension that couldn't quite take full form in this universe.
I sometimes see them much more clearly and hear them whisper when I'm trying to sleep. Sometimes it is impossible to sleep with all the noise.