This is sounding like harmonic balancer. I didn't get the memo about only when warm.

Two examples of "belt like squeak" sound but only when warm ended up being harmonic balancer on XO

To test: get car warmed up and squeaking and then remove belt and see if it goes away.

Search for the two threads using advanced and "harmonic balancer" in the content. Two in the past year on xo.

You can also use an app like FFT to listen using earbud microphone so you can home in on the source.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)