One thing I have noticed with every cell phone I have ever used is it depends a lot on the source. I usually go to ZEDGE for my ringtones and notification sounds, because I can find some that are literally twice as loud as anything that comes with the phone, all else being equal. With music or video, I find streaming the content never plays as loud as if the content is local. Also make sure you have the correct slider at max volume (eg. media for music/movies or ringtone/notification for those two). If you can barely hear it and you are 100% sure it's at max volume, try some other sources and notification sounds. If you can still barely hear it, maybe your device is defective.