(Posting back with an update from earlier post)
Well, my Seagate Momentus arrived today. Took out Scorpio Blue(Two screws now worryingly stripped - have a replacement set of screws on order from Apple)and got the Seagate in.
Happy to say that it's a distinct improvement, although not totally silent. The clicking sound(as described perfectly by several posts)has thankfully gone and that was the biggie for me as it was beginning to wind me up. The other noise - the constant 'whooshing', is still there but noticably less so than the Scorpio, to the extent that although still audible, it's now so faintly there that it is not in the least distracting. I only heard it when I took my Mac into the quietest room, my bedroom, and to be honest then it kinda felt more as though it was simply a faint hum, or, in Sci-Fi lingo, the Very Pulse of the Machine!
In short, I'm happy. One day we'll all have large SSD's in there and this(for some)problem, will be no more.