The front microphone is really weird/ Taking time to start

Hello, just got a used iphone xs max. Everything is working perfectly, I’ve even changed the screen.

But there’s something really weird : when I disable the stereo recording on front camera the front mic takes like 2 or 3 seconds to start. I explain my self: by “start” I mean we cannot hear a thing during 2 or 3 seconds except a weird noise which sounds like the wind. After these 2 or 3 seconds I can perfectly hear myself during the whole record.

It’s the same for Siri (without the Hey Siri) : it doesnt detect my voice during 2 or 3 seconds then it perfectly works, also the same for the voice keyboard.

But the weirdest thing: when I try to enable “Hey Siri” it doesnt detect my voice at all even after 2 or 3 seconds.

On the app “Phone Diagnostics” it cannot detect the front microphone.

I’ve already tried to clean the front microphone with a toothbrush etc but it doesnt change. What can I do please ?