I never posted on this forum, but it is so annoying that I have to post.
Same problem for me. It is really really annoying when people send me multiple texts, and I get angry at them just because of this defect.
I went to the Apple store twice. First time, the guy noticed it within less than a second by hearing it. He brought it inside and actually "TRIED" to fix it for about 30 minutes. He came back out, and it was gone! I was really happy, but unfortunately, it came back after a week.
So I decided to go back again and ask for a new phone. This time, a girl was helping me. She just said she didn't hear any sound, and she brought it into the back. Only this time, she came out 5 minutes (I'm not sure if she even tried) and said everything looked fine. She even mentioned her manager said nothing sounded wrong.
Shame on Apple genius bar. Literally playing deaf with me. Apple does make fantastic product, but I'm definitely surprised by their service. If they can't cover all their defects with warranty, just DON'T cover them! Can't believe I bought apple care+ for nothing. They refused to repair it or give me a refurb.
Share you experience here! Don't let this thread die away!