Fiesta Zetec pre-igniting?

commonly the cat breaks up and rattles, a good thump on a speed hump will usually cause it and a good thump with a fist will make it rattle, shaking it is not enough unless it is off the car.

Thanks. Will attempt to thump it.

See if there is a dead hairy animal coming out of your exhaust pipe.

Now that you mention it, I do hear a faint meow every now and again. I always blamed the auxiliary belt.

I've not thumped the cat yet (can't find a good way of actually getting close to the bloody thing), but I noticed the middle section of the heat shield has come adrift. It can be shaken about, but sounds rather tinnier than it does from the inside (assuming that it is the cause of the noise). Trouble is, I can't see how it's meant to be held in place. I can't see any of those funny flat nuts that hold the rear section in place. Are you familiar with this thing?

can't remember off hand, but certainly it should not be flapping, but I doubt it would make much noise.

BTW, do you suppose it's possible to take the oxygen sensor out, and try to rattle it through the hole in the top? Or would there be something in the way?

Inside the cat there are usually two pieces of cat material, generally it is the rear one that detatches, removing the next downwind bit of exhaust may allow you to see the end of the cat material and ascertain if it is loose.

I have several times cut the cat open, removed the loose bit and welded them back up again, they still work ok.

Removing the O2 sensor can be seriously difficult, but you might be lucky, I don't know that you will have enough access even with it out.

Do you mean difficult from an access POV (I know some of these are underneath, but mine's on top, in plain view), or because they sometimes feel like they're welded in place, or that they are extremely delicate? I have good access to it, so if that's the only problem, it would not have cost too much to try it. But if there are reasons to leave it well alone, I'll just get underneath and undo some bits of exhaust pipe.