Microphone feedback Problems

[iamdmc]

I'm wondering why my mic gives me feedback (especially when the system resumes from standby or hibernation). It's very loud!

I tried to disable the mic (using the vista sound properties)
I tried to mute the mic (using the vista sound manager)

Both did not turn off the mic!

What can I do? I don't want the feedback! It's a brand new system, so it shouldn't be doing this.