Possibly this. I have an LG Optimus Elite and it will not let me turn off the camera shutter either. In a lot of places in America (I don't know about other countries) it is illegal to take pictures without the shutter sound, that way people aren't taking pictures secretly. Because of this, companies just don't give you the option. You have to root and delete it manually, or use other apps that will allow you to take pics without the sound.
Dude I am using MMX A87 from last few weeks and I also realize that we cant switch off the camera shutter sound from its settings.That's why I am using this little app and it is working perfectly but it works with rooted phones only