I heard a little rattle underneath my car one day,and pushed it off for later.Later turned into a week,and now it's louder.I jacked it up today,thinking it might be bad,and my passenger side cat has a consistent knock/rattle noise.It might be the heat sheild,but it dosen't feel loose.Anyone else have/had this kind of problem. Mike

 

That sounds like a good candidate for the old catalytic converter "death rattle". If it is indeed coming from the cat, it's on its last leg. If that's the case it's best to replace it/get rid of it before it becomes a MAJOR restriction to the exhaust. Before simply replacing I would also try to find the cause. Quite often there is a misfire that overheats the cat.

 

I don't think I have a misfire,how would that effect the cat.Is the rattle coming from the honeycomb coming apart.

 

Misfire causes a false lean condition, the PCM dumps more fuel, excess O2 and fuel is oxidized by the cat. The cat literally starts to melt down from all the heat and eventually collapses in on itself. The catalyst material can also plug mufflers, depending on the type.

This is not always the case but a dying cat can be an indication of an ignition problem. It's best to look ahead of the immediate problem or you might be revisiting it in the future

Yes, as the catalyst honeycomb breaks down it rattles in the case.

 

The cat in my car fell apart the day after i bought my Z, left me on the side of the highway overheating...lucky my buddy was behind me for a ride...anyways, get the cat changed so it doesnt clog your exhaust, because it happens real fast when it falls apart....

 

Could be the ceramic crap broke. Cats are spendy. See if you can pick one up off this site where someone as ditched theirs, or call your local yard.

Best to call ahead to see if they have one at a pull-it-yourself place. Seems like you'd get a better price if you called, since they might lose a sale if don't like their quote.JMHO

 

When my cat rattled, I just went underneath the car with a broom handle and just banged the cat. Took the car for a drive...still there. Then I went WOT, and the sound was gone Hasn't been there since.

 

Just put the car on a lift,then take a rubber mallot and bang the cat,if you can hear stuf rattling around,replace the cat.When the cat does fall apart,it ends up in the muffler,so replace the cat with a HIGH Flow cat,and a muffler of your choice.Hope this helps.