Firstly, make sure you are adjusting the volume in the phone's settings - not just in the media player or anything. Secondly, try a different ringtone if you haven't already - the one you're using may just be a bit of a quiet one. If it's none of these problems, it's probably an audio driver issue. The best way to get this fixed is just to send it off and have it replaced. There are ways you can do it yourself through modding the phone and though it is fairly easy to do, it will void your warrenty.