Bottom mic not working when speaker is attached

Hi,

I have this strange problem with 2 iphone 4s devices. I replace the bottom microphone including the 30pin dockconnector. Before putting back the bottom speaker I always check if the new parts are working correctly. After booting the phone, I'll run and microphone test with the recorder app. Great, mic works. Then a charging test, also working. Time to put al parts together and run a final test. Again, booting up the recorder app, and strangely de mic ain't working...

After some tests the mic seems to works when de bottom speaker is not touching the charge/mic flex cable. When i'm lifting up the speaker 0,5mm from the bottom right corner (when display is facing down) the mic works. As soon as i push it down, the mic doesn't work any more.

Ofcourse I tried a new flexcable, but this results in the same weird problem.

I'm out of options to try and can't find anything similar on the web. Hopefully someone here can help me :)