I have a bad left primary, and found a secondary for cheap $$$. Are the primary and secondary cats on the C32 interchangeable? Thanks!

no i dont think so.

no

Nope-thats why the secondary is cheap a$$
Primaries are the ones you "need" to have on the car-the seconds are (worthelss) for show.
I swear. Thats all they are for.

Crap. Looks like another hole in the pocket is coming.

how many miles do you have on your car ?

62K. I have been experiencing a "clatter" or metallic rattle noise from the left underside of the engine. I happens mainly at idle. I thought it was heat shielding or something hitting the exhaust pipe, but the mechanic just told me that it is the driver-side primary and that some of the honeycomb has broken off and is rattling around.

If it's anything like the Non-AMG cars- what most people talk about as being secondary "cats", are actually small bullet mufflers/resonators.

Resonators don't have honeycombs. You should be able to have it done under warranty I think it's 8 years 80k miles.

hey dont worry just take it to mercedes, they will change it out for you for free. maybe even do both sides for you. cats are under warranty for up to 8 years. i should know, it happened to me too.