The test with Sound Recorder is critical. If you DON'T hear the screechy/underwater noise in a Sound Recorder recording (and I would test by launching a game during a recording), but folks on the other end of a Skype conversation with you report the noise, it is likely a transmission problem on your end or a reception problem on their end. If you both turn off the Skype video, do they still report poor audio quality from you in the conversation?
For your Skype conversations, are you using ethernet or wireless. If wireless, is it b/g or n?
On the other hand, if the Sound Recorder recording test gives poor quality audio on playback of the recording, you're looking at a faulty microphone or possibly an audio driver issue.
G74SX-A1 - stock hardware - BIOS 202 - 2nd Monitor VISIO VF551XVT
