Share your experience!
are you near any TVs or speakers? does this happen with youtube or any other music app?
I'm sorry to hear this, you should contact your local Xperia Care.
http://support.sonymobile.com/global-en/contactUs/
Before you send it back or exchange it, you could
check if you experience the same issue while on safe mode
http://talk.sonymobile.com/t5/FAQ/How-to-boot-your-phone-into-safe-mode/m-p/348008#U348008
or reinstall the latest update with PCC
Bridge (for Mac)
Alternatives on How to backup Xperias