so, i changed the timing belt yesterday and changed the tensioner and idler pulley while i was at it. The water pump was weeping out of the 'tell tale' hole so i replaced it as well.
It would have been approximately a 4 hour job, but my mate that was helping me accidently snapped off one of the 6mm bolts that holds the top timing cover on. Then it turned into a big mission to find a small enough ezi-out kit in town. And in the end I ended up drilling out the bolt and tapping it to an 8x1.25 hole instead and now its all sweet.
Anyways, now the new belt is fitted, the whirring noise that was there before, is now completely gone :-)
There is now the higher pitched whining/whirring noise... which is obviously characteristic of a new timing belt until it runs in.
But other than that, everything looks fine.