I have noticed this ever since I got my phone. The headphone jack will not get a clear connection with most headphones I use, especially AUX cords. This causes either a muffled sound or a static hiss. I thought it was a software problem at first since PowerAmp corrected the problem (for awhile) but yesterday it totally stopped working. I'm pretty sure the connectors inside the jack are screwed up and always were. So if you have this problem right after buying (or replacing) your ZIO go get it replaced ASAP since there's a 24 hour limit on returns with Cricket (not sure about Sprint). I've seen posts of other people with this problem. It's a factory flaw for sure. In the future don't buy a ZIO (or any Kyocera product) if you have a choice in the matter. Now I'm off to the store to pay the $20 to get it replaced. -_-"