Thanks all for the suggestions, I had looked for but could not find any drivers for either the Sony or Pioneer drives. However, there is more recent frimware (for both), which I have tried on the Sony.
Interestingly, the result of that was to provoke the same - undesirable - behaviour on XP!
Reverted the firmware and restored config. and it's quiet again (in XP).
The suggestions have provoked a few more thoughts, so I have a few more things to try.
SD