Hi CMCMC,
Thank you for using the Apple Support Communities! I understand you are experiencing a sound concern with your AirPods Pro, and I'd like to help.
There are a few things I'd like to have you test out, to see if it impacts this sound you are describing:
-Are you hearing this sound while in standby, or while on a call or listening to different media?
-Does the sound go away or change when you adjust the volume lower?
-Do you hear this sound when you have a certain noise-control mode enabled, or do you hear it with all three noise-control modes? AirPods Pro Active Noise Cancellation and Transparency mode - Apple Support.
-If you pair your AirPods Pro with another compatible device, do you hear the same sound? Connect and use your AirPods and AirPods Pro - Apple Support.
Keep me posted by replying back with responses to the above questions.
Regards.