There are two types of bangs, one is when the airbag pops (very rare) and it's very loud. The other is the pressure valve on the compressor opening to release the excess pressure...it's not loud but very clear and sound just like it says on the tin
Either one of them will trigger the warning message on the dash and results in the car lowering itself but not deflating the airbags completely (other than the punctured one of course).