Hi just to bring up something. Have had some rattles coming from the rear of my MK2 punto, they only happen on slighty bumpy roads and make a louder noise on really bad roads.

few things i checked, and did.

Check locks on rear seats - fiatboo.co.uk/fix-a-bravo.htm#interior (i cant add links yet so add www. to the beginning)
as posted by chrisuk in another thread.

Parcel shelf knocking (not the problem) - ensured of rubber bits where in place to cushion parcel shelf (i added two small strips of foam insulation tape. like you use of doors, to help cushion it better)

Tool tray - tighten like rambo on steriods (not the problem)

Thighten all screws holding interior - plastic speaker sections etc (you will see them if you look, im not good at explaining these things) found a screw was missing replaced with new screw.

check wiring loom and boot lock release cable is fixed down in the clips under the carpet near lock in boot. add some electrical tape to ensure it will not become unstuck (my were unstuck, and had a slight knocking against bodywork)

check rubber bits in each corner of the boot/tailgate.

and finally,

tighten the bolts that hold the lock mechanism to the tailgate, mine needed tightening which was the problem, and that caused the boot to make a banging noise. (well a knocking rattle type sound.

may come in handy for some one

try driving down a road with no windows open, no radio on and no blowers/Air con to source your rattle. remove parcel shelf and do the same and put rear seats down and do the same you should find you annoying rattles

hope this is of use to some one.