Share your experience!
You have some call options,from there disable microphone noise suppression.
Look for slow talk also.Check if the same problem occurs in safe mode:
http://talk.sonymobile.com/t5/FAQ/How-to-boot-your-phone-into-safe-mode/m-p/348008
How is it in safe mode?
Strange,you might have a 3rd party app acting up.Do you have task killers,battery savers?