So when driving I have a really annoying rattle coming from the back of the car. I've checked the boot, nothing I can see to make a noise. Checked the rear seats are locked in properly, no issues. I'm settling on the idea it could be the rear wiper tapping against the window. Anyone had anything like this??

Tools in the wheel well under the boot ?

The Parents 500 has an occasional rattle from the piece of plastic that runs along the very top of the boot, near the rear part of the headlining. It looks like the plastic that covers the wiring etc for the high level brake-light.

I noticed ours rattling on rough roads when I was sat in the back of the car a few weeks ago, but when in the front I can't hear it. It's more of a buzz on ours than a rattle, but it does get a bit annoying when in the back. Pressing on it did shut it up, but gave me a numb arm after a while!

Could it be the hatch (boot) internal cover , if you lightly tap around the edges of it there may be some movement. I had similar issue and used a self adhesive pad between the cover and hatch to remove the movement.

Check the passenger side seat belt, sometimes if its been twisted as it reels in it can spin round and tap on the door pillar. The tapping can sometimes sound like its coming from the back.