I would like to assist you with troubleshooting your DROID Charge!
I need more information to provide you the best resolution for your situation. When you say the sound fades or drops, is this happening when on calls, or when playing music or audio files? The issue with the screen entering multiple characters, is it only happening in your bill payment application, or does this happen in multiple applications such as email or texting applications? Are you using any 3rd party keyboard applications? Have you tried soft resetting your device?
Please let me know so I can further assist.