This was feature which I always hate - phone made strange sound when taking photo. Fortunately I'm not alone who hates this and there are several howtos on net which should guide you to do this.
The only way which worked for me at the end was replacing sounds in
phone filesystem, so that it plays silent sounds. For Sony-Ericsson
K750i with CID 49 BROWN you need specially hacked FAR from
SE-tuning.cz and just replace files in filesystem
/tpa/preset/system/sound). Now phone magically makes no
sounds when taking photos :-).