Well, not so much a rattle actually, more an occasional creaking/grumbling from under the boot floor that started a few weeks ago and has started to become more regular and pronounced in the last few days. The other symptom is a very occasional sound like a pop - best way I can describe it is like something (balljoint, nut and bolt etc) being put under tension and suddenly popping out of position (or back in to position), which mostly seems to happen under extreme vertical travel at the back (like an aggressive standing start causing the back to squat, or when I took a tight uphill left turn at speed causing the back NS wheel to become unloaded).

Both springs, shocks and top mounts were replaced a couple of years ago. Droplinks are Meyle HD and about 2 years old. The look and feel OK.

Could be the rear ARB bushes. They are showing signs of perishing.

Other bushes appear OK. The only two that concern me are (I don't know the right names for them), the big one at the front of what I'd call the trailing arm, where it joins the subframe near the front of the arch, and the one on the other end of that same 'link' or arm where it joins the hub. Both look OK but there is a small amount, like maybe 1mm, of movement with some levering. I don't know how much movement is acceptable though. Looks like a subframe off job (and hydrualic press) to do that front bush so god help me if that one is gone as that's going to be a big bill!