Catalytic Converters

[Alexlind123]

Can worn cats make an uneven/intermittant rattling noise at idle only when very hot? If not, im beginning to think that something is very wrong with my engine. Although with 110k thats hard to imagine.

[Kobe Diesel]

The heat shield attached to your cat converter might be hanging on by a thread. If the shield is loose, this will rattle when the car is running.

[Alexlind123]

Possible, but unlikely. It only does it after i have drive the car a long distance, and even shutting it off for 10 minutes is enough for it to quit making the noise when the engine is turned on again.

[Kobe Diesel]

Ticking sounds from the car's exhaust after it is shut down can be heard as it is cooling down. It's the contraction of the steel.

[Alexlind123]

I dont think i was being very clear. When i get home from school, the car usually makes an increasingly loud rattling noise while idling. Today when i got home, i started my car up again after about ten minutes to show my brother the noise, it didnt make the noise, presumably since it had had time to cool.

[Kobe Diesel]

If you have tools, jack and jack stand, and the time - it's always hard to find time - lift the car up and take a look at your exhaust system. Check the rubber hangers in the rear, the flange connections, heat shield, look for holes, rust, leaks, etc.

Yesterday I found a big hole in the rear silencer and removed the rusted heat shield from the cat.

Everytime I get underneath this thing I find something to do. Well it is a 17 yr old car.

[onewhippedpuppy]

I have heard of shot cats rattling internally, something in there rusts out and rattles around. I know if I bang on mine from underneath, it sounds like it's full of marbles. Magnaflow, here I come.........

[mikell]

The honeycomb in the cat can come loose, and it sounds like rocks in a tin can. It may not affect the catalytic function, but could drive you nuts. One guy told me it was because an internal component that secures the honeycomb got too hot and basically burned away, and he theorized that was because the motor was running lean. Guess what? turns out my engine was running lean 'cos of some gunked up injectors.