"Rubbery squeaking" from rear of W215 cabin

My car has developed an annoying "squeak" in the last week.
I haven't managed to track it down yet, but let me explain it.

The noise occurs only when the rear suspension is exercised differently on each side and front to back. It doesn't occur when driving over sleeping policemen or speed humps (even if only driven over on one side). Bouncing the car up and down manually doesn't appear to produce the noise.

It's quite load inside the cabin and appears to emanate from around the rear seat back area. It sounds like rubber parts rubbing together (think of rubbing two balloons together) although it could be leather trim against something.

Has anyone any ideas?

Failing that any idea of how I can remove the rear seats in order to eliminate or confirm them as a cause of the noise?

 

There are release levers each side on each corner for the seat release base, pull the lever upwards

 

Just an update.

I've finally located the "rubbery squeek" or as my wife put it "the sound of two S&M squirrels in latex suits!"

It turns out that at some point the top part of the n/s/r ABC strut, concertina, boot has come adrift and caught between the bodywork and the strut itself. Over the past few weeks, as the noise has become louder, this boot has been merrily shredding itself.

As it wasn't protecting the strut anymore I cut off the top, shredded section and now all is quiet.

I gather that the boot is available if bought with a strut, so I'm left with leaving it until it fails (if it actually does).

In the meantime, I'm willing to pay a reasonable price for a good condition second hand boot, but I suspect that they're as easy to find as rocking horse poo!