People can hear themselves when I talk

[killakakashi]

So I've searched and searched and I can't seem to find the answer to this. It's come to my attention that whenever I talk on vent, if someone is talking at the same time they can faintly hear themselves over my mic.

I'm using the Mac Version of Ventrilo, a USB Logitech Headset and I've tried everything but I can't fix the problem. If anyone can give me some insight into this, that'd be great, it's driving me nuts.