Sorry Robin i meant to reply earlier, been rushing around a bit tonight... I changed the rear sub bushes myself about 4 thousand miles ago because of a similar (yet less frequent noise). They were TOAST! I checked the new ones again recently because i thought i might have ripped them out by driving a bit too sprightly one day when i managed to loose my cool. However they look fine and i replaced the four little bolts and the two big nuts while i was there and cleaned the plate and sprayed it with and undercarriage protector.

Thanks Whisky (could just go for a JD right now!), i'm hoping there's someone experienced in the art of shocks/mounts as it looks grim on the passenger side (RHD) who can give me some more hints/tips.