For some odd reason, my AirPod Pros are doing this weird thing. It is in transparency mode or noise cancellation mode, and all of a sudden the sound goes more transparent, to the point where it sounds like a microphone that I can hear myself through.

If you have the 2nd generation AirPods, this might be due to them having adaptive noise cancelling; where it automatically adjusts the strength of the ANC to best fit its own needs. To mitigate this, I can refer you to an article I found to be extremely helpful regarding ANC issues; The AirPods Pro 2 ANC, Strong when It Wants To: How to Improve It? - NoisyWorld

Something to also note, is that iOS 17 included a major update to AirPods, bringing a new feature called conversation awareness. This setting automatically switches between transparency from ANC whenever you speak, so make sure this isn't enabled.