small part near proximity flex cable assembly

Hi, I was taking apart my iphone4 to replace the proximity flex cable and and when i took the cable and speaker out a small black part also came out and I have no idea where to put it back! its about 6mm long 2mm thick and has a small loop at one end. one side is flat and the other has little compartments sunk in. I have looked at lots of guides but cant see where it has come from and cant put my iphone back together until i know where this goes! if anyone knows what im on about please help!! Thanks