Why does my EVO 3D think I am talking to it?
The connector must be a bit loose (or incorrectly sized) and as it wiggles around in the socket, it hits the connectors in a way that makes the phone think it's equipped with a mic (that is, a TRRS plug instead of TRS). Try another pair of headphones or try twisting and aligning the plug/cord so that there no pull or twist in the root of the cord.