I had this, drove me insane... Took every single piece of trim out of the boot several times, WD40d the rubber seals, took the locking mechanism apart, spare wheel, rear lights etc out... no luck. Then when I was fitting the reversing camera I found a little plastic popper for the trim was hidden away somewhere I wouldnt have seen it when I originally took the boot apart- It was this that was making the squeaking! Felt like such a tool