Subaru have found what my knocking noise is.... Rear shock! Did suggest this when it first went back but they said my shocks were fine. Apparently it's the left hand side rear shock and strut brace, which is now on order.
I asked if the other side was likely to go aswell, to which he replied "who knows, seems ok at the moment" Won't be impressed if i get it back for a couple of weeks then the dreaded knocking noise returns.
Shouldn't it be normal practice to change both rear shocks? Especially with it being a common fault on the 03 sti.

Cheers for the info.

David.