What could possibly cause my sound problems after reassembling?

Hi all,

I have the following problem:

I changed the proximity sensor/power button flex cable in my iPhone 4 GSM device and reassembled it. The power button works, but some additional problems came up...

- When talking to others on the phone, they are extremely quiet (tested with different partners).

- When talking on speaker phone, they cannot hear me.

EVERYTHING else works fine (did a long extensive testing).

I noticed that the piece marked with the red arrow on the uploaded picture is damaged. It broke at around the red line. It has not come off, but it is definitely not in original state.

http://imageshack.us/scaled/landing/826/...

What does that piece do? Could that cause my problems? What else could have gone wrong?

Thanks in advance!