91 200tq Exhaust Rattle in Cats?

["Peter Dowker" <pdowker@mindspring.com>]

Any body with a clue on this?

  I have a funny rattle in the exhaust system. When I first heard it, my heart skipped a beat and I thought " o no, not the turbo..."  The car is 200 tq, 91, 128 k 
miles, reasonable condition.  Noise sounds like a loose flap or pebbles in a can, sort of a rhythmical clank, varies with speed (road speed/rpm can't tell - though 
when I drop it into neutral while slowing for a stop, and boost the gas, I get no apparent reaction from the noise).

I've found that the spring loaded retaining screw apparatus (no idea of the real name) that connects the catalytic converter to the exhaust system pipe heading 
toward the muffler ) was loose on one side, and needed to be tightened. Eh, voila, il a disparu (the noise went away) for 3 days....

Hmmm... do I need to think about catalytic replacement - worst case - if so, which ones should I look at?  I have the Stebro SS exhaust on the beast.
Do I need to replace the retaining screw things? (such technical jargon -amazing how illiterate one is without the manuals/fiche). Do I need to learn the names 
of the parts in question?

Any help would be gratefully received.

Thanks in advance.

Regards,

Peter Dowker

'91 200tq Tornado Red
UFO Conversion, SS exhaust
Looking for Euro-Lights