I have the FRE case for the 6s. I don't have any issues with people hearing me, but I also make sure that all ports and speakers are clear of any dust etc. I also make sure the case is totally clean as well before I put it on each time. As for the warranty, its great! My first FRE case for the 6s had a tiny gap where the two pieces of the case come together on one side. It still passed the water test but I was worried that over time it may be an issue. I called Lifeproof and told them about it and they sent me a new case. No questions asked. No proof of purchase needed and I didn't have to send the old one back either. I know that the sound issue/muffled speaker issue is something they are aware of and will definitely replace the case for you if you give them a call! So far I am very pleased.
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