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You probably damaged the second microphone
settings > about phone > diagnosticst > test > microphone
Not that I can think of, but you can contact your local Xperia Care
you could share such video to another phone and test it, just to narrow down the issue.
Contact your local Xperia Support
http://support.sonymobile.com/global-en/contactUs/
My understanding that the secondary microphone is to cancel the noise
http://support.sonymobile.com/global-en/xperiac3/userguide/Phone-overview-D2502/