Hey there, buckandjack!
We appreciate you reaching out on Apple Support Communities. From our understanding, your AirPods Pro microphone seems to be having some sound quality issues when being used with your MacBook Pro. We’d be happy to look into this with you.
You mentioned that an NVRAM reset seems to temporarily resolve the behavior. So that we can fully isolate this, we’d like to have you test the AirPods Pro using the right microphone, then the left microphone. Does the behavior occur with both microphones, or just one? You can check this by clicking on the Apple menu > System Preferences > Bluetooth > Click on “Options” next to your AirPods Pro. From there, next to microphone, you’ll want to select each AirPod and test to see if the behavior occurs with both.
If it appears to be occurring with only one of the AirPods Pro, follow: If your left or right AirPod isn't working
If that doesn’t resolve it, we’d suggest resetting your AirPods Pro as well using: Reset your AirPods
If it occurs with both AirPods Pro, we’d recommend checking for any interference that may be contributing to the behavior using: Resolve Wi-Fi and Bluetooth issues caused by wireless interference
Lastly, if the above steps do not help, try connecting the AirPods Pro to a different computer, does the same behavior occur? If you connect a different Bluetooth device to the Mac, are you experiencing similar symptoms?
Let us know if that helps.
Cheers!