How to get rid of static with interal microphone?

So I have an inspiron 1520 and dell keeps replacing my microphone and its getting old. People can hear me, but they also hear a lot of background static so they can't fully hear me. Dell claims its fine, but when I use ventrilo or skype it happens again and again.  I also have a headset with a microphone attached to it, but it does the same thing. It's almost like my computer isn't disabling the internal microphone and its trying to use both. I know its not just the headset because this has happened with multiple headsets. So I was wondering if there was a way to either get rid of the static with the internal microphone or if there's a way to disable the internal microphone so I can use my headset.