Well firstly the mic should be fully extended at all times, but I'm sure you do this already.
Other than that, go into Accessory settings, make sure the "voice changer" setting is set in the middle, neutral.
Also try turning on and off, HQ mode for the headset.
That's all I can suggest really.
Try switching USB ports with the receiver and testing again.
Hopefully it's not that you got a bad microphone.
