My cats on my 08 2lt starting going out and rattling at idle and was getting worse and worse (2nd set of cat after stock one) I ended up buying a ZZP down pipe (2.5” no cats) and I had a resonator delete done at a exhaust shop prior to the down pipe ( running stock muffler) and now it sounds decent at low rpms and idle but it sounds like a Honda after 3k rpm on up....
would a resonator or a glass pack at where the resonator at help quiet down the raspiness??

my car sounded decent with a down pipe (the one with two cats ( gutted the 2nd cat out)with a resonator delete)

 

I like the sound level with a 24 inch resonator and stock muffler.

 

Just curious:
Why did you buy a 2 cat pipe if you intended to core the second cat? Didn't know that 2006-2007 only had 1?
What happens with the #2 O2 sensor? Just put up with the CEL?

 

My 08 hhr has a single cat originally (flex pipe cracked) and I didn’t have access to a welder so I bought a whole down pipe with cats and the one I got had two and the 2nd cat was rattling while idling and I got annoyed at it and gutted it. Then the first cat started getting clogged and rattling so I got a zzp down pipe and I don’t have a CEL I have a o2 spacer bung thinking about removing the sensor completely (if I recall you can make it so the rear 02 doesn’t read at all)

 

What is killing the cats? Are you ignoring something, doing it on purpose? I have never heard of anyone killing 2 and very rarely 1. Is the CEL burnt out?

 

No CEL functions properly, I think because I bought eBay cheap cats for a temporary replacement

 

A bad cat should have lit up a P0420, at least. The only way to turn the sensor off is with some sort of off road tune.

 

I do recall seeing that code long ago but solved the issue by putting a O2 spacer.
i am not running cats now but still trying to find a solution to the raspy Honda fart can sound....

 

The cat would soften the sounds.

 

You will need a cat or a big resonator as OldBlue mentioned or it's gonna sound rough.

Cats don't get normally killed quickly unless there's coolant or oil in your exhaust.

I used a 24" resonator on my catless autocross car (not an HHR, but it was a 2.5 NA car) with a Magnaflow muffler, and it wasn't too bad. It killed the worst of the droning. Of course, I wanted something I could hear with a helmet on... With a stock muffler, you really shouldn't have that much noise.