My husband and I both have the same issue (S9 and S9+ respectively), and it's REALLY annoying because we use speaker phone 90+% of the time (car, 3 kids at home). They're both brand new, T-Mobile, not unlocked if that matters. Sounds like the person on the other end is distantly under water, and gets worse as the conversation goes on so that it becomes almost 100% of the time. It's often ok for the first few minutes, but not always. We just upgraded from our S7 phones that we had zero issue with, using them in the same way. Anyone figure anything out yet?
Yep I'm having this issue with my S9. My husband hates for me to talk to him using speaker phone because he can't understand what I'm saying most of the time.