I don't recall ever not having ringing in my ears. When I was really little, I thought that's what people meant by "silence."
Also, I can hear cathode ray tubes, old radio tubes, and used to be able to hear ALL fluorescent lights. The only way you're going to find out if it's something she's actually hearing is to have an all out full blown hearing test done. Ask them to test supposedly non-audible frequencies. You might be surprised what they find.
If they don't find anything, it's probably tinnitus.
My wife can hear dog whistles.
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I'm not likely to be around much longer. As before when I first signed up here years ago, I'm finding that after a long hiatus, and after only a few days back on here, I'm spending way too much time here again already. So I'm requesting my account be locked, banned or whatever. It's just time. Until then, well, I dunno...