OK so others can learn from this heres what I did: without changing anything a placed a audio CD in the dvd drive to hear the sound reproduction. Sounded great. I then did what was suggested and play the same dvd using a different dvd software player.
The sound was greatly improved infact no obvious problems. With this sw playing I checked CPU utilization to be approx 80-90%. Played using original software (power dvd ver 6.0) again and sound problem returned where CPU utilization was more like 90-95%.
I also tried reduced the graphics screen resolution and played dvd again using power dvd software. Interestingly the sound improved but still heard some small amount of crackeling.
Funny that my IBM labtop using power dvd software plays same dvd with no problem however obviously the dvd drives between each system are different.
Thanks to all as I feel I'm getting closer to some form of resolution or confidence in the purchase of the drive. Your further comments are welcome.