Not trying the hijack the thread, just reporting some facts (please delete if required).
I often get sound issues with PD.
I can record directly from the camera and no sound will play back during recording, however the sound has been captured fine in the resulting file. On these occasions I have to reboot my PC before the PC will produce any sound at all. It's like PD disabled the sound card.
I did a recording the other day (again with no sound), the resulting video file did have sound (as usual) but this time it was just pops and crackles and nothing else.
I'm running Vista 64 with a Creative Labs Audigy 2 sound card. I know that Creative driver support for Vista 64 is poor so I'm looking to change sound card. Hopefully this will sort the problem out.