(Easy to reproduce with the help of another person.)
1. Acquire a 4-five .45 and attach a suppressor on it.
2. Shoot towards your friend and ask if he can hear a sonic crack.
3. Acquire a ACP-C2 .45 and attach a suppressor on it.
4. Shoot towards your friend and ask if he can hear a sonic crack.
5. Acquire a Vermin SMG .45 ACP and attach a suppressor on it.
6. Shoot towards your friend and ask if he can hear a sonic crack.