Hotfeet said:
I believe I found the culprit... It turns out that Norton Internet Security has a defragmentation program that runs on the boot volume. For those interested, the exact setting is: Idle Time Optimizer.

I disabled this feature.

Thanks
Thank you for posting your results Hotfeet. turned out to be the simplist of things but something easily overlooked
Posting your result really helps others if they pick up this thread in a search
Best wishes for Xmas & New year