I have the revving up and down issue on all MSI B450 boards (as do many others) with any cooler unless I set an unreasonably flat fan curve or just peg it at a fixed percentage. The only difference with the high end coolers is their effective speed is slower and quieter so it's barely noticeable.
I have been feeling like there's an issue with the board/BIOS/AGESA's PID control algorithm.
For what it's worth, my cooler settings were broken with MSI B450 BIOSes (I've got a Mortar) from the point they shrunk the code (with the new UI) to make room for Zen 2. But the last BIOS with the old UI is perfectly fine
I have been feeling like there's an issue with the board/BIOS/AGESA's PID control algorithm.