Clanging noise

[feetn2veg]

I have an ominous clanging sound coming from the rear of my 2003 2.0Hdi when hitting a bump in the road. It sounds a bit like a couple of steel rods coming together in the boot. I've checked the boot and there aren't any steel rods in there or under the seats. In fact I've stripped out everything from the car that is moveable, including the spare wheel and its carrier. I've been under the back end and nothing is loose or obviously broken. The exhaust is tightly in place. All 3 rear doors work properly and don't appear to have anything inside to make a noise. Not many miles ago the MOT found nothing amiss and just showed an advisory that the rear axle was corroded. The car looks straight and runs straight. There is no new continuous 'running' noise. Could a failing back axle be producing such sharp clangs?

[oilyrag]

Maybe torsion bar issue?

[ffrenchie]

My exhaust was making a noise but it seemed solid. One of the back box rubbers was split and let the exhaust twist when it was given a really firm tug. It did look like it was doing it's job as it was above the box and hard to inspect.

[Gadgetman]

Check the rear axle subframe. 
Jack the car up by the jack points on the body and support it. 

Is the rear of the frame hanging down?    

   

There's one of these at each or the rear corners. 
The outer two holes mount it to the subframe, the hole in the middle is to connect it to the car body. 
Sometimes the rubber fails and separates from the metal frame around it. Then the entire frame and axle will pivot around the front mounts(which are a bit less... fail... )   
Note that the ENTIRE subframe is pivoting, and that includes the torsion bars and shock absorbers. 

The blocks aren't all that expensive, and it's done in minutes to replace them as long as you get the car jacked up. 

Only issue is the bolt in the middle. It needs to be tightened by using a long, thin torx you insert into a vertical hole in the frame.

[feetn2veg]

Many thanks to oilyrag; ffrenchie and Gadgetman.
A quick look under the car revealed nothing to me EXCEPT that it's time for me to give up looking under cars! It's too painful!!
However the ideas you've come up with will help me talk to a mechanic and appear knowledgeable. I will ask him to check out the things you've mentioned.
Thanks again!