I would guess that the mic is a condensor type. These mics are much more sensitive to transients, and they tend to pick up a lot of ambient sound around them. In contrast, dynamic mics, such as the Shure SM 58 have become the standard live mic because their pickup pattern and response tend to be concentrated close to the singer, thus rejecting the ambient noise that condensors pick up. The live sound environment is very different acoustically than the controlled studio environment, and therefore, mics are chosen to accommodate the different acoustics.