I also have a knocking from the rear, I suspect its either the exhaust or a top mount, but haven't been bothered to look at it yet (and it wasn't apparently on the smooth roads of the test drive).
The other thing I've noticed is that when labouring (low rpm, higher gear etc.) there is occasionally a very slight bearing noise, so I'll have to wait and see how that develops - I've had cars in the family with noisy input bearings go for 50k without any issues, or getting worse, so it may just be fine - of course, I guess it could just be the clutch release bearing sticking, or even just need the oil topping up changing - this will be my first port of call, seeing as its cheap and easy.