I just replace my palm pre at the sprint store after my first one completed locked up and crashed.

I'm assuming the "new" phone is a refurbished one. Every since I got the "new" phone people have said they have a hard time hearing me. Is this a glitch with the mircophone or is there a way to adjust the microphone sensitivity? Or is it back to the sprint store for a repair? I have the latest software update 1.4.5

Thanks for the help!