Quick Time 7 - converting avi file to iTunes

Hi

I purchased a copy of Quick Time 7 (version 7.6.6) in order to convert some avi video files I have to m4v so i can see them on Apple TV.

The QT7 seemed to work and convert files ok. Last week when i converted my Christmas video the picture came through OK, but the audio was all wrong and had a rythmic rasping thud overlaid on the sound which sounds a bit like a metallic drum beat The avi file plays normally in Quick Time and the sound is fine, so I am assuming there is a problem with the conversion process.

i have never had issues before so wondering what has gone wrong.

Can anyone help?

Thanks

Caroline