Turn up the microphone volume in the Sound Control, and make sure that both the inline volume control are turned up, and that nothing is muted.
all volumes are turned up and muted, it's not really a matter of volume, more "sound detection". it doesn't pick up any sound until I blow into it or put it in my mouth and talk, and then the volume seems normal.
whistling as loud as I could with the mic at normal position didn't do anything, the microphone didn't seem to recognize the sound.
it may be a part of the system's "noise cancelling" procedures acting over the top... though I don't know much about this...