Same porblem.
My solution: (Although not good, I hope somebody has better idea.)
Use "Line In" instead of Aux or CD input. Still some noise but a little better.
OR
1. after recording, separate the audio from the video, then noise reduction.
2. combine the audio and video.
This way the audio has some distortion after noise reduction anyway.
Is there anybody can find me a good audio noise reduction software?