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.

---

[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.

Phyphox is a great sensor suite app for undergrad Physics experiments, and it includes a spectrum analyzer. Also, it supports both iOS and Android.