I finally figured out what this buzzing noise was that I could hear in the car when I would accelerate sometimes. It was getting common enough that when I started my car yesterday I could clearly hear the exhaust rattling while I stood outside my car. The only thing I have done to it was a zzp 3" catted downpipe and it still has the stock catback and exhaust manifold on. Nothing appears to be loose, anything I should look at while I have it up in the air?

 

Sub'd.

Slightly different set up, but I just noticed last night that I get exhaust rattle when I'm idling with the AC on...

 

check the heat shield, its probably touching somewhere, you can bend the stuff pretty easy so its farther away from the pipe. mine did it too. does it sounds like this? you can hear it from :11 to :13

YouTube - ‪Cobalt ss exhaust‬‏

 

It sounds similar to that. Mine sounds like it's coming from the middle of the car, over by the glove box area. I will have to take a look underneath this weekend.

 

that vid is the exact sound my lsj makes only when idling

 

yeah mine did it when idling only on cold start idk why. my exhaust was touching a part of the heat shieldl, bent it away and its gone.

 

yep betting on heat shielding. i had to bend mine to get my badmab pipe to fit, my 02 sensor was touching it.

 

Last night I had it up in the air and bent away the heat shield next to the converter because it seemed like it would be touching there since it was so close. Well, I left for work this morning, still same rattle, and it seems to be getting worse, now i can hear it in every gear while accelerating. Get home tonight and don't notice anything with the heat shield so I start hitting the downpipe with my hand and it seems like something was actually inside the dowpipe. The downpipe is fairly new (March 17th of this year) and Magnaflow makes good stuff but what are the chances of the cat actually falling apart from the inside? I know stock ones will do this but a new one that only a few months old??

 

magnaflow? i thought it was zzp? and its possible but who knows.

 

It's a zzp 3" catted downpipe, and I thought they used magnaflow catalytic converters on their downpipes? Either way I need to contact them to see what they think.

 

i had a bad exhaust rattle but found it was a loose o2 sensor.

 

im not sure. if anything just take it off and look inside. all the bolts are tight and everything? front and rear gaskets both in?

 

Yeah, the o2's, and all the bolts are tight and no leaks at the gaskets. I would if I had extra gaskets, I might go by autozone tomorrow to see what they have.

 

yeah heat shield was for me too

 

i could be by the exhaust, thats where mine was touching but that was my mpx exhaust not stock.

 

Found the culprit today... the heat shield that is attached to the catalytic converter itself. All of the spot welds were broke except for 1 corner, so I just pulled it off. I'm assuming the stock heat shield should be good enough without this on?

 

im sure youll be fine.

 

i dont see why u would have a problem. I mean look at me just to put my zzp mid length header on i had to take off the stock heat sheild lol it wouldnt fit ...my car runs fine