Why are balloons so loud when they pop?

Ever heard of a jet breaking the sound barrier (traveling faster than sound) and causing a sonic boom? Simply put a balloon popping creates a small sonic boom.  You take an inflated balloon and make a hole in the latex, the energy released by the balloon in form of air, or gas, from inside the balloon expands the whole in the latex faster than the speed of sound. It is the hole expanding faster than the speed of sound in the air which breaks the sound barrier causing a sonic boom.

Do you have idea what the first man made object was that could break the sound barrier?

A whip.  The sound you hear when the whip cracks is a sonic boom.  Balloons weren't invented until 1824.  We may not know when whips were invented, but it was definately before balloons.