Hi, Guys!
Thanks for all of your comments and suggestions!
The problem is now solved.
AndrewP : You were right!
The factory chain was far too long.
I checked the length as per Shimano's recommendations and found it was 4 links too long.
I guess it is like the famous court scene in the TV series 'The Odd Couple', where Feleix is before a white-board and says, "When you assume you make an ass out of you and me (ass-u-me).
Anyhow, with the chain off I re-adjusted the high and low end stops and then re-installed the chain.
I then adjusted the B-tension.
Shifting is now almost silent and is as smooth as silk.
Much better than when I first bought the bike.
I guess the factory must had set-up things in a bodgy way originally.
Grand Bols : Thank you very much for answering my original question. It is appreciated.
Again thanks to all of you for your help.
Regards,
Roger