Wondered how many of you have got this problem.
Its plasticy creaking sound that seems to come from the seat cushion (bit your arse sits on) side bolster nearest the door. Tends to make itself heard mainly on right hand bends as your weight shifts to the left. It sounds like a nut has come loose and rolling about - but I don't think it is that.
I've tried spraying wd40 under the seat, but its not solved it. My next step was going to be looking under the seat to see if some sort of nut needs to be tightened.