Rattle from under the boot area

[smithy_sid]

I own as second hand 2023 Mk4 Jazz I love it, but it has an annoying rattle which appears to be coming from the rear of the car around the offside boot area. It's only audible if driving at less than 15mph on uneven ground. Above that speed, and on smooth roads, it can't be heard; I assume that road noise drowns it out. I've tried all the usual tricks to try and locate it: emptying the boot; removing the tyre kit from its cubby hole; attaching all the seat belts; driving with rear seats raised; driving with rear seat backs lowered. All to no avail.
 
The car handles perfectly, and it sailed through its MOT. My local (independent) garage checked the underside of the car for any suspension/drive shaft/exhaust/heat shield issues but couldn't find any problems. They could hear the rattle so I knew I wasn't going mad, but said that they didn't think that there were any safety issues. They said that the only thing they could think of doing next would be to completely remove the lining of the boot to see if there was anything rattling around under the boot.
Has anyone else come across this problem? I don't even know what's under the boot area or how to remove the lining.
Any suggestions would be gratefully received.

[Marco1979]

It might be the magic seats; if one of the metal parts has a little room it can jiggle in its mounts. First check is to see if the rattle stops with the seats upright. A little tape where the seat clicks in will solve it.
Good luck and enjoy your Jazz!

[Kremmen]

Also, fasten the rear seat belts as a test

The metal fastener can easily vibrate against the hard plastic it rests against

I've been putting some of the fluffy side of 2" black velcro where the belt buckle rests on quite a few cars

[Lord Voltermore]

When you say you removed the tyre kit from its cubby hole  I assume you mean the side cubby hole, but did you also  check the under floor store compartment?     Did you fully check everything in the side cubby hole  . My 2021 car came with quite a few bits in there that could rattle  if not strapped in securely.   
I also added a few extra tools etc of my own, carefully wrapped and secured.  The previous owner may have done the same  and something has slipped down  out of sight.

 Incidentally my 2024 facelift car had fewer accesories in the compartment.  No reflective triangle for instance.  (Unless mine had been 'purloined' ) I didnt query it  at the time as I already had 2 others.   

[Lord Voltermore]

I agree ,try a bit of tape  where seat back and magic seats may jiggle in their mounts. Or experiment by jamming in temporary wedges ,or bracing  potential movement with a cable tie etc .     Even if it just changes the tone of the rattle you will know you are on the right track .

[ninanina]

I also had an annoying rattle from the rear of my ‘23 Jazz. It turned out to be the right hand side cubbyhole in the boot where the repair kit is located

There is a roll (which if I remember correctly contains some tools) which is strapped vertically with a tie strap around it but the strap wasn’t tight enough to hold it off the below metalwork

As soon as I tightened it up off the metalwork the rattle stopped