I have a pair of s6 and a t10 that have been abused but remain flawless for many years now. My buddy got a pair last year at my suggest, and one of his s6 is doing what you describe. It has a hollow sound and seems like most upper range is missing. A reset did not fix the issue. The speaker has about 4 hours of use. I am currently looking into repair or replacement for him. So in short: Yes, someone else has also encountered this issue.