Share your experience!
Boot the phone in safe mode,see if the same occurs:
http://talk.sonymobile.com/t5/FAQ/How-to-boot-your-phone-into-safe-mode/m-p/348008
You should take a look in call options and disable microphone noise suppression.About the phone,the touchscreen works perfectly in safe mode you say?
There must be an app acting up.Any task killers,battery savers?
Antivirus?If you cannot identify the problem,you got to try a software repair.
No call options to disable?Maybe speaker voice enhancement.