The last couple of days my Pre2 has become quiet. Ringtones are set to full volume but sound as if they're set to a 1/3. The device is so quiet I cannot even here the whoosh of cards leaving the screen.
This has happened on my pre2 more times than I can count and a restart always fixed it for me. If you've tried that and it didn't work also make sure its not stuck in headset mode and then if all else fails time to visit the dr.