Rattles

I had a job interview last friday, was running late, as usual. Fired the rangey up, to be met with a loud rattle. Shut it off, got rest my stuff together, check oil and water, all ok. Started back up, still doing it. Had no other transport, so decided to just go for it. Go there ok, and it seemed to have stopped. Was ok when I left and went home. Went out saturday, and it fine all day. Went out in the evening and it doing it again, loudly. Sunday I foung a HT lead had come adrift and was laying in top manifold. Changed the leads, found couple plugs loose, so re tightened them, all was good. Used it monday and it fine. Didnt move again till wednesday, ok. Nipped out in it last night and doing it again. Ghecked all plugs and leads, noise seens to be goming fron underneath. I ran out of petrol other week, and im worrying that I killed the cats? Is it possible, or anyone got any ideas? I dont realy want drive it too much, incase do more damage, but I need to use it tomorrow for 50 mile round trip.

Ran ok saturday. slight rattle, not too bad. Brother in law used to be a mechanic, he reckoned it sounded like the cat. Pulled exhaust off yesterday from y pipe, took it for a spin up shop. Only a 2 min drive. Over the roar of running no silencers can still hear a slight rattle, but not as bad. Got under and it def coming from the near side cat. Replacement ordered and arriving tomorrow. What the easiest way to extract the old? I have got them to send me a set of bolts so am planning to try to shear the bolts off, but what is the easiest way to extract them? Im thinking of recip saw the pipe after cat?