Hey Timothy
You don't mention how old your Zed is? If its after 2006 the top won't lock down on UK models.
I have a 2006 and had a really annoying squeaky type rattle similar to yours - turned out to be the locator for the plastic parcel shelf. Easy way I found it was to go inside the boot and on the rear wall in the centre directly underneath the parcel shelf is a kind of slot that the lug on the parcel shelf slides up and down in. I moved it with my hand and it replicated the squeak. Cured by lining the slot with some neatly cut soft velcro to stop the plastic -metal rubbing.
2 months later I got another squeaky rattle that I couldn't cure and neither could my dealer. Seemed to be coming from deep inside the panel behind the seats - another dealer found the cause. It was a badly adjusted boot catch!
Do you have the OEM fixed wind deflector? I have that along with the plastic screens that live inside of the roll hoops. My drivers one buzzes like crazy (not really squeak though) so could it be that? I cured my passenger one with the ever faithful soft velcro but now the driver side one is doing it too!
Best of luck, please let us know how you get on!