GD1

I recently purcased a used Zafira Tourer 2014 reg 1.4 petrol turbo. Over the last couple of weeks I have noticed some intermittent creaks and clonks from the rear. The noises don't seem to be dependent on braking, accelerating, going over bumbs or repeat at regular intervals. My local MOT Centre have looked at the car and assured me that its not a brakes, wheels or a suspension issue but can't figure out what the cause is. The noises are more likely to be present after a cold, overnight start driving at irregular speeds on local roads, less likely when driving at a regular speed on dual carriageways or motorways. Any suggestions as to the possible cause will be very welcome