Facetime for Mac Issue

For some reason, I've had issues with facetime for Mac when my Macbook is connected to an external monitor. I cannot be heard in my discussion, and the mute is not on. Any help on this? I saw a similar issue someone was having when facetime was still in beta, but it was never resolved.

A few things:

The mic works fine through iChat when connected to the monitor.

The mic works fine when not connected to the monitor.

There is no additional speaker or external mic on the monitor.

The app was working fine, and I think it stopped functioning properly after the most recent update.

I have reinstalled my facetime app.

When i try to ensure it is set on the internal mic, it will not allow me to check it off, no matter how many times I click it.

Yes, I'm sure its on my end, it doesn't work properly when in a conversation with a friend's mac or on my own iPhone 4.