Capturing from a tape-based miniDV does not change the audio or video information in any way, Unkie. So if you're capturing from a miniDV camcorder and getting distortion, that distortion is happening in the camcorder itself.
But if you're getting distortion when you output your video, it could well be because your audio levels are too high.
As I say in my books, whenever you edit your video, you should go to the Window menu and open the Audio Mixer. Watch your audio levels as you play back your timeline. They should peak at Zero. If they're up in the yellow and red or are overloading the mixer, you are going to get distortion in your video output.
But if you're saying you're hearing distortion while capturing your video -- that's a whole other issue. You need to adjust your computer's audio levels or turn down your speakers. As I've said, capturing over FireWire does absolutely nothing to change the audio or video information that's coming in from the camcorder. It's just your computer playing it too loud.
I think Steve meant "As I've said, capturing over FireWire does absolutely nothing to change . . "
Is the same item on the tape OK when you play the video directly into a TV set?
Is the soiund distorted while you are capturing it or only when you preview a clip of it?
Is everything you transfer garbled or only some items.
Wind blowing across the microphome in the camera can cause sound like you describe.