A bit of back story here ... Over the winter I wore out an exhaust gasket. At the time I wasn't sure which one it was, or if it was a blown cat, or hair line crack in the header. Regardless, I went and replaced everything. All three gaskets (Head-header, header-dp, and DP-catback) with OEM gaskets from GMPD. Also scored a Bad Mab header, and a low miles (compared to mine) stock DP for my 3 good 18" tires. The install as a whole went great. Pretty easy thanks to a Dremel here and there on rusted over bolts. I tightened everything down and let the engine idle for about 15 minutes, saw some smoke leak here and there and shut it off, and retightened everything again with no obvious exhaust leaks (Noise or fumes).

Now fast forward to the last couple weeks. I found my down stream (post-cat) O2 sensor was only in the hole because it was wedged in against the undercarriage. I thought that was the rattle, being the lock washer on the sensor vibrating freely so I rethreaded the hole and put a new O2 sensor in and turned it all the way down, and checked the pre cat (up stream) O2, which was very tight in the header. I have turned all the header bolts down a couple more clicks of my socket wrench 2 or 3 times now, and triple checked the 3 bolts in the header/dp connection and the two just after the post cat O2.

I have also replaced the SC coupler (ZZP) and the timing chain tensioner with the new style (CED).

The rattle ONLY occurs between 2000 and 2400 rpms. And anything over 3k rpm sounds great and perfectly normal. Sadly this is right where most of my down town/cruising is done, so I'm forced to be in 2nd or 4th when I'd like to be in 3rd, etc. My mileage and WOT power/boost haven't changed, minus the improvements from the header.

Sorry for this wall of text, but I like to be thorough to wade passed as many questions as possible. Thanks guys!!

 

Did you check to see that it's not warped?

 

Check your resonator....

My resonator on my Corsa catback crapped out on me, and caused a rattle at low rpms.

 

The header? No but I have tightened all the bolts down basically as hard as I can go with the size wrench I can get behind the engine, unless I am missing one elusive bolt after all these attempts.

It looked OK prior to installing, and the previous owner had no issues with it.

Edit ... Resonator, not cat ... lol I have not checked that. How would I do so?

 

Remove downpipe.

Shine a light inside of the resonator. Also, you can tap on it with a rubber mallet and listen for rattles.

Mine did not rattle until it reached operating temp, so the mallet trick did not work for me.

 

Now that you mention operating temps, the rattle is quieter when its at normal operating temps. What would I be looking for in said resonator? Chunks broken off?

 

The resonator is straight through, but there are perforations in and around the inside that cancel out the bad tones. Depending on how it is put together, they may be broken, and causing the rattle.



Note: The stock resonator is a little different, but what I'm talking about going bad is the same. Notice the broking tabs.

 

also the pesky heat shield above the downpipe and in tunnel can come loose or even get rock and whatnot in it. free to check so why not.

 

Yes. Good idea to check. That's what I thought my problem was at first. I added a self tapping screw at each mounting point.

 

OK So back from the dead, this rattle is still there, not getting any worse, but still annoying. I took off the top row of bolts one by one, sprayed with lube and retightened again, the rattle is still there. Time to take the bottom ones off. Now I was thinking ... Could the plate from the BadMab header be THINNER than the stock header, making the bolts bottom out in the head? The bolts feels very snug against the header so I wouldn't think so, but its a thought worth asking. Also since I'm tired of this rattle, I'm going to change the bolts I'm using on the header/DP gasket as well, maybe a washer on there is loose. I'm going to try to get original bolts for that.

 

Nope. I ran the Badmab at one time with no issues.

Usually a rattle in the exhaust is caused by a busted cat, resonator, or heat shield.

Check all of your hangers as well.

 

OK awesome. TY for clearing that up. Heat shield is off, spark plug cover is off, and loosened, penetrated, and retightened various bolts around holding hoses in place too. Just hitting every possible loose end. About to go get new bolts for the Header/DB and will update in an hour or so.

Updated: I haven't gotten bolts for the DP yet, but after retightening all but the last 3 bolts on the drivers side, the vibration has but cut in half, and goes away completely much faster. I also found that these double ended bolts work at lot better when I thread the bolt in and let it bottom out, and then put the nut on over it. I think once I do this to the last three, the vibs *HOPEFULLY* will be gone, but I had a broken washer on the DP that was still held on, so I will replace all nuts, bolts, and washers there to cover my basis.

 

All is well after an hour or so of removing each bolt individually, threading the bolt down with the spine socket until it ran out of threads, then put the nut down afterwards, let it idle for about 5 minutes, then retorqued. It runs nice and quiet now! I need to thank Staged07SS for answering basically every question I asked in this thread over the last few months! Thank you very much!