Location Microphone issue in recording

hi guys,
I have a problem with my lg g pad, exactly about the microphone. When I record audio or video have a problem with mute noise. something like a second microphone problem. but all I know there is no second microphone in lg g pad. I tried to change something in build.prop in the audio settings, but it gave no effect.
you know what could be the reason?
I put a sample below and sorry for my english


i cant place link because i don't have 10 posts. but i must place it, do not be angry ;c