Noticed that at tickover, when hot, the left hand cat is rattling, or, more accurately, clonking. Common fault?

Had this with my Classic - had the cat cut out and a new one wleded in - job done and alot cheaper than an original cat !

I'm thinking that ill just get one off the bay for about £200 - when the rattling gets to annoy me enough. Atthemoment you can only hear it with the window open, and winters coming.

An old problem.....

Click image to enlarge

My car was almost new in those days...

What about screwing a few big self tappers in the side of the cat?? Would that hold stuff in place until you replace it? Or, as I suspect, is this a stupid idea!  Previously..
Vogue SE TD6
Defender 90 2.4
Defender 110 TD5
Vogue 3.5 EFI

It could be the spot welds on the heat shield have snapped and that is causing the noise if so either get it re welded or take the heat sheild off as it won't do any harm (unless you park over a lot of long grass when the exhaust is really hot)
Roger