Just a quick note about rattly pumps. Mine had been knocking for ages and I'd been on this forum looking at various ways of sorting it.I'd just about decided to get a genuine VW one after all the horror stories about the cheap ones on fleabay and then got some info about the angle they're fitted isn't the way Pierburg (the manufacturers of the pump) designed them to be fitted. Evidently because of the angle they're fitted oil gets behind the piston over a period of time and stops the piston returning fully so more clearance for the pump pushrod.........and we know what that means................nasty rattle!! Anyway decided to do it yesterday so pump off and to the bench.Took the 6 Torx bolts out and took the plate off, it's not under load or anything but there's some seals and valves there so either take a note of what goes where or take some photos.When you've got that lot out of the way put a 15mm socket in the vice,put the end of the piston rod in it and undo the nut on the other end(11mm spanner) Leave a few threads to go then just take the tension off by clamping it up in the vice. Now you can remove the nut,open the vice and remove the piston rod and spring. The only thing now holding the piston is friction so either clout it on a wooden surface or poke it out from behind. The piston has a stepped nylon seal so take care of it.Now the interesting bit, mine had less than a teaspoon of oil behind the piston so I wasn't convinced that oil was the problem but I carried on and cleaned the oil up.Putting it back together is just a reversal of the way it came apart,making sure you get all the valves in correctly(I think they'll only go in the right way). I realised that something had changed when I started to fit it back on.............because the piston was now returning fully the overall length of the piston rod and the separate pushrod was now longer making it just a little more awkward to fit!! Got it all back together and fired it up and............rattle's gone!!!!! Acess is a pig so it's not the easiest job to do but so far so good. Maybe it'll get oil behind again but I reckon it's worth a try for the money I've saved!!