I am pretty sure it's my smog pump. I have a grindy - rattly sound coming from that corner of the car but I haven't pinpointed it.

I've hit the cat with a rubber mallet and do not here any rattling.

But the rattling seems to happen off and on for short periods during driving. It is not entirely random. I will pull up to a parking spot and its rattling but then after idling for a few seconds the rattling stops and does not come back unless I drive (revving the engine does not do it). It's also not the kind of rattle that a single loose catalytic brick makes. It's like more than one piece.

Also, the rattle does not change in pitch with RPM but it does seem to rattle faster.

Some of these symptoms take me to a broken cat, but others to the pump. Neither is cheap to replace.

Any thoughts?

 

If you have v-belts? Just remove the belt to isolate the air pump.

 

Yup, pop the belt off, eeeeezy enough to do the math from there.

DO NOT hallucinate that you can just leave the belt off indefinitely!!! You will need to do something more permanent, one way or another.

Your description sounds more like the cat heat shield is broken loose though. Not the innards; just the heat shield. You can also just get up under the car after it's cooled down and bonk on the pipes right next to the cat and see if you can force it to confess its sins.

 

Thanks, I will hit the pipe ahead of the cat. I have a serpentine belt. I suppose I could pop the belt off and drive for a minute but I gotta be quick- no water pump.