iPhone 5s no sound/audio from buzzer/speaker
 

Hi folks,

I face the following problem:
I don´t get no sound out of the buzzer/speaker.
It´s neither stuck in headphone-mode nor muted.
The headphones work fine, and the speaker at the top works as well.
It also recognizes the headphones when I plug them in and also when I unplug them.
But:
If I click on a ringtone and hold the phone near my ear, I can softly hear a noise (it´s just a rush-sound, not the sound It´s actually playing).
But it does the same thing when the headphones are plugged in. So I think the connection is fine.


Here´s what I´ve already tried to fix this:
-swapped the buzzer/speaker (twice)
-exchanged the buzzer/power-flex cable
-complete reset
-restored it to an older iOS version
-went through all settings and checked if the sound gets routed to another device

I definitely need your help!

FYI: I´m familiar with electronics and I have equipment to measure or solder, so any hint or experience will be appreciated!