Why won't my iPhone record noise at concerts?

This has been going on since 2014. My iPhone 6 rarely records noise at concerts. At first I thought it was my bulky Otter Box case, but I have found that taking it off makes no difference. Every time I get home from a concert, I find all my recordings to be visually good, but all I hear is a faint noise that sounds like when you plug in earphones when nothing is playing - so it's not even a faint sound of the concert. However, all four of my snapchat videos had clear sound! And if the videos from my camera roll do have sound, it's only about three seconds in the beginning.

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