A client car had a tensioner that was worn on the pivot point to where it was bent 2-3° and causing the belt to ride off the edge of at least one pulley.
I removed the tensioner and used a right angle grinder to bevel the face that mounts to the "engine" (not sure if actually the block or what), and got the thing to pull straight again.
Back to topic: I would use a microphone on an earbud wire etc and an app that does FFT: you will see the exact spike in some frequency related to the squeak and makes it super easy to find.
An example: I was using an air compressor and was hearing a strange noise like a mosquito; it bounced off everything so I could not tell the direction of the source at all!
FFT caught the exact tone and I just waved my phone around to home in on the source: was a hose fitting that didn't have enough Teflon tape.
https://apps.apple.com/gb/app/fft/id298840058
That is the exact app I use.
This is another option I think it's cheaper maybe free (odd thing with app store is that it doesn't show price after purchase).
https://apps.apple.com/us/app/sonic-...m/id1245046029