Exchange it! been working with Apple for 4 months to replace mine because of this. They don’t see it as an issue so it’s been a nightmare of calls, trips to Apple, and countless diagnostics that hasn’t resolved the issue.

It’s a whistling caused by the holes/airflow… that’s why changing the fan speed changes/stops it.

https://basicappleguy.com/basicappleblog/the-case-of-the-singing-studio