I had to have my original S23 Ultra replaced for this same infuriating issue
@DuncAlexander. The device was new, and right from the start it's audio quality on recorded video was very poor at times. Like you said, it sounded like it was recorded under water in many situations. I am with EE, and got my device from them. They agreed that my complaint was valid and sent me a replacement device within 24 hours. This device had no such issues and Is still going strong some 18 months later.