Microphone on Nexus 4 doesn't work

Since many months the microphone on my Nexus 4 doesn't work, except when it does, which is occasionally.

In Loudspeaker mode it works always, I believe, but in the camera, phone calls or in memo-apps or even in google now there is only this rustling or random noise...

I've tried the Soundabout "Fix", rebooting in Safe mode and last month I sent it back to LG where the "replaced the insides".

The problem persists...

Does anyone know what to do next? Send it in once more?

Please help! :(

Example video: