How to record video from MacBook Pro with its associated audio using Quicktime without room 'noise'...

I need to record a video from the screen on my macbook pro and I am using Quicktime. If I want to record the screen with its associated audio, but do not want any room "noise" how can I do this?

Additionally, is there a way to have the audio from the video record without having to listen to it from the computer (e.g. can I mute it?). I tried it with selecting 'internal audio' and muting the computer but when it records with the computer muted it only records room 'noise'.

Thanks for any help!