There is a clunking noise from the axle when I have people in the back, or a lot of stuff in the boot and I am slowing down or coasting. It's been like that for quite a while.
Does anyone have any ideas on what it could be?

 

shock absorber?

rubber coupling for propeller?

transmission support?

the sixpack beer inside the trunk?

 

On my old 380SE, the shocks were completely gone, and I had the same noise you describe. Try getting those checked out. If it is the beer, be careful when you open it.