I just did a quick search for you on this forum, and the speaker problem on the S20 Ultra seems to be quite an issue!!!
Below is a link of serveral other S20 Ultra owners dealing with the "same problem". Obviously this is a warranty issue, and you'll want to make sure that Samsung warranties each replacement phone for another year (at least the speaker component). Your speaker should get warrantied after each replacement for another year since it's a known problem. - - Good luck!
Be sure to click "✓ Accept as Solution" when you find an answer that works for you. - Thanks!
Have you tried changing the audio quality using the equalizer in your settings? Give this link a try: https://www.samsung.com/us/support/answer/ANS00080348/
Be sure to click " ✓ Accept as Solution" when you find an answer that works for you.
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