Langoliers Mic

I have 2 microphones, one desk mic that I used to use, and a headset mic (Plantronics) which is new.

When I use push-to-talk, I'm told that I just can't be heard.

When I have it constantly transmit, some quiet rumbling starts which gets louder and louder eventually becoming deafeningly annoying. :|

I have tested it myself in Steam's 'test mic balance' and hear the same thing. This happens in all programs, on both mics.

I have tried using windows settings to adjust volume levels, I've unplugged and re-plugged the mics into several different ports. Nothing works. Bear in mind that I have an audio switcher, which has my speakers and headset plugged into them, so that I can switch from the two.

Any help would be appreaciated, I will post any information that you may need.