I wish could rent one to figure out which device in my office has a squealing capacitor. I can hear it well enough to be driven crazy by it, but not well enough to find it. I start disconnecting things to narrow it down but then convince myself that it's my ears ringing.

I'm unsure if I'll age out of this problem, or if worse hearing will just recreate it at different thresholds.

You might have some luck with a spectrum analyzer app[1]. A fixed-pitch whine should show up as a line on the waterfall graph. If you move the phone around to differently locations, you might see the line getting stronger or weaker. You can also try rotating the phone to different orientations to see if it is coming from a particular direction.

I used this to locate an annoying squeal coming from some equipment at work once. And to confirm that it wasn't imaginary.

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[1] On Android, I like these two:

Spectroid (https://play.google.com/store/apps/details?id=org.intoorbit....). If you use this, consider turning on the waterfall display in the settings.

Spectral Audio Analyzer (https://play.google.com/store/apps/details?id=radonsoft.net....). This has more color options for the waterfall display.