iPhone 6 plus video sound problem

I have a problem with sound on videos that are recorded with my iPhone6 plus.

here is example:

http://youtu.be/NJwIT3Kwyt4

this is happening from time to time. I Noticed that this is happening when I am recording some type of music concerts (I assume that high input volume causing this problem).

I Hope that some could help me.

Regards,

Igor