I have a rattle that is most evident when the engine is just started and is still slightly lumpy. It feels like it's under the driver's feet. You don't notice it when driving.

MOT bloke said it's most likely the CAT come lose inside the exhaust as he never noticed anything else while doing his inspection. Does this sound likely? If so how can it still work. It passed ok on emissions.

Mud Flap said:

I have a rattle that is most evident when the engine is just started and is still slightly lumpy. It feels like it's under the driver's feet. You don't notice it when driving.

MOT bloke said it's most likely the CAT come lose inside the exhaust as he never noticed anything else while doing his inspection. Does this sound likely? If so how can it still work. It passed ok on emissions.

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The catalyst can come loose inside the housing and it would cause a rattle. You can hear it if you bang the outside of the housing with your hand. If it is still in place then it does work on the gasses passing through the exhaust.


The problem occurs when the honeycomb is so badly damaged that it can move to the side inside the housing in which case the engine cannot breathe and you can get exhaust blows and gaskets blowing out even complete non running.

You hear it the minute the engine is cranked over but as it heats up the noise tends to disappear.

B