I hear the same tick sound, i think it's ok.
Turn all sounds off and check if it's coming from a part inside the phone or the camera shutter (i think it's this,not totally sure though).
By the way, can you hear some other rattling,creaky noise when you tap the top part of the screen with your finger or when you put your phone down on the table, desk etc?
relative thread : http://talk.sonymobile.com/thread/50135
