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It's hard to say from here if it's something wrong or not. Have you tried with different ringtones? You could also try to boot your phone into safe mode to see if there are any difference:
http://talk.sonymobile.com/t5/FAQ/How-to-boot-your-phone-into-safe-mode/m-p/348008
Otherwise, I suggest (if possible) that you compare your Xperia Ion with another Xperia Ion to see if they have the same volume.
You can always try a software repair to exclude software related problems. But if you still experience low sound, I can only suggest you to compare your unit with another Xperia Ion.
Or that you contact nearest service center so a technician can examine your unit. You can contact your local support team for further information about nearest service center and/or how to proceed with this in the best possible way:
http://www.sonymobile.com/global-en/support/contact-us/contact-info/