Hi Fidget, I recently part ex'd my 02 Moneo LX. It had also suffered the symptoms you describe, it knocked and creaked from the rear when going over bumps / pot holes. I took it to my local (non dealer) garage who told me it was the subframe bushes, but they couldn't fix it and recommended I return it to Ford. They couldn't do it because it would require re-aligning the subframe, which they didn't have the equipment for - that suggests to me that, in answer to one of your questions, it's not a home job. He also said it would cost me around £500, that was two years or so ago so your quote is not far off the mark. I also asked him what the consequences were of not having it repaired - to which he replied "you'll have an annoying knocking". Well, I lived with that knocking until the last day I had it and became very good at avoiding potholes! If i'd have had the money though, I'd have had the work done.