Generally, there is a small hole on the back side of
the iPhone, but some other phones it exists on
the front side, near to the front camera. This tiny
hole is called “Noise Cancelling Microphone”.
When we call from our iPhone in a fully noisy area
but the receiver end doesn’t listen to any noise,
cause of the special audio system present in iPhone
called “Noise cancellation System”.
It also helps a when clicking pictures, by eliminating
pixel noise. It is suggested that we do not cover this
microphone in any possible way. Covering it would
affect noise cancellation.