Very interesting. I can remember being able to hear a high pitched tone when I was 4-6 shopping with my mother in department stores that seemed to get louder when we approached flush mounted speakers in the ceiling. This article measures the frequencies and explains it's a normally operating feature of the systems.
Going into Sears used to drive me nuts. My parents finally accepted that I was actually hearing something that they couldn’t, but it took a while. I don’t know if it was the loss prevention system that was doing it, or what. All I could do was localize it down to being anywhere remotely close to the entrances. And the closer you got, the louder it got. These days, my tinnitus is constantly ringing at about that same…
Exactly this. When I was 17 I worked at a JC Penny store as a stock boy. Every time I approached certain entrances (like the main one that opened into the shopping mall) and other areas of the store my ears were assaulted with a high pitch squeal. Never figured out what it was, nobody else seemed to hear it. I've always had tinnitus, and the frequency always seemed to be the same. In fact, I'm listening to it now.