|Thanks both, appreciate that helpful advice.|
I've eliminated the HD as a candidate, as the delay remains at 8-10 s after unplugging it.
I was hesitating about an SR as I'm a bit vague about other (wanted) changes I may have made recently. But I'm going to give it a try. Can always restore back. Otherwise looks like I'm going to have to master that rarher daunting ShellExView and methodically test my very large number of context menu entries. Upside is that it will motivate me to get rid of a lot that I never use - providing I can learn how to do so safely.
Terry, East Grinstead, UK