Some environments aren't suited for a loud camera shutter, Weddings being a prime example.
A mirrorless camera system is virtually silent. Good times! But DSLRs aren't.
Luckily, camera brands have introduced quiet mode (to some camera bodies) and this significantly decreases the shutter sound.
You'd have to check if your camera has it and what the setting for it is, but on Nikon bodies it's a 'Q' on the program dial.