Alot of camera phones do the same thing so you can't disable the sound.  When I got my phone in HK I was told that it was to try and prevent "discreet" pictures of unsuspecting women, like upskirt pictures I guess.  Some vendors even offer to get rid of the sound for an extra fee when you buy the phone.  It must be a big problems in cities like that, which is understandable when the city is built skyward.