I am having call quality problems with my new 5s. For instance, when I make calls from my office desk, people on the other end often complain that they can't understand me at all--due to static and poor call quality. When I made calls from that same location with my iPhone 4, I could be heard perfectly. I get a strong signal from at&t at that location so it's not a signal issue. Has anybody else experienced this with the 5s? Is this a known issue? What can I do? Thank you!