Microphone or sound record issue

[AlexandreVegetaroux]

Hello, I own a remi3s but I want to expand the question to other remi3 user. could anybody help me to test the record feature of the redmi 3s because I notice an issue. If I record in several Apps a sound like a long permanently humm sound, the sound record perfectly for the first couple of seconds (2sec) and after that the sound level lowers down. Even if I use the field recorder app or the in build Miui Audio recorder I notice that the led indicator of the Audio signal lowers. And than the record is very bumpy during a permanently sound like hum or somthing else. Only if I talk the record is very clear and nearly perfect.
Whats this strange level lowering of the recird signal during hum souns.
By the way I need surch records, because I am an audio engineer.

please could anybody test it on miui or cm based roms

Thanks