have noticed a rumbling sound coming from the passenger underside. As though my front muffler was loose, will 5take to a mechanic to lift it and see what is rumbling. Pray it is not the converter do they give fair warning when defective?

if it's cold outside or at first start up, peek underneath and see if any heat/steam/vapour is escaping any part of the exhaust. Loose joints such as headpipe to cat. flange. The bolt flanges rot off and the seal leaks.

I don't know about 'fair warning', after all, they've had to hold on to the bottom of a car in all sorts of weather for years, so what's really 'fair' here? grin

But I have seen pics of pins or long screws through some cats, that were used to hold the matrix in place after it was detached from the body and rattling around inside.

Yes, the baffles rattling around is definitely one sign...:)

To the original poster: With the engine cold you might be able to shake the cat yourself and listen for rattles. Or with engine running get close (but don't touch! - very hot!) and listen for rattling.

Also look for cracks. The cat on my 240 cracked on top and the crack slowly worked its way down until it was almost ready to split open like a coconut!

BTW - Aftermarket cats aren't too expensive.