Exhaust Rattle on start up only
 

When I start the car, for the first 5 seconds the exhaust rasp is horrible/tinny sounding like a heat shield is loose at the muffler area. I've crawled around and looked/grabbed stuff and nothing is loose.

It only does it on the first start up of the day. Any ideas? It's annoying but not that big of a deal.

2011 touring sport - 2300 miles, OEM exhaust system.

Funny you should mention that. I have a 2011 coupe and it does the same thing. Its like the exhaust has to warm up and and seal then becomes quite. Usually last about 30 seconds or so. I have not looked around under the car etc. at this time.

I rarely drive the car so I was wondering if that was an issue in getting the exhaust to seal etc. Currently the car has 887 miles on it and mainly sets in the garage. I might drive it next week to the dealership and ask them to check it out. I wonder if anyone else has seen or heard of this possible minor issue. I will let you know if I get any insite or resolutions from the dealership.

2011 blk/blk Sport M6, 887miles, no mods

Its something the car does to warm the Cats up faster, I think almost every new car does it but they all make different sounds. Dont worry its normal, you should hear my moms 2010 Forester XT Sounds like the thing is running on two cylinders with no oil.

Run it by the dealer.

Usually it happens when the exhaust is just a tad loose, and it goes way once everything expands. The dealer should take care of it though

I'm telling you guys its normal, nothing is lose. How would it only rattle for 5 seconds then stop???? Its a warm up cycle.

It's not normal to rattle on the stock exhaust.


The reason it goes away is the pipe expands, but if it's rattling cold, it is also slightly loose when hot. Not a problem, but it's annoying.

Because its not actually a rattle he is hearing, it just sounds like a rattle. You should hear my car now on startup. Its a very strange sound because its doing some kind of warm up cylce.

OP it makes the weird sounds then kind of fades away right???????

ehh, my 350z does it in the morning lately, but my exhaust is aftermarket, no cats. the gaskets/bolts up by the headers back out sometime..which is why people shy away from aftermarket headers on the 350. I'm in tune with my Z, I can notice when the hiss on decel from the testpipes is too significant, the gaskets get worn or the bolt is a tad loose in my case. I would have them look up by the cats, assuming the 370z cats are formed the same way..if you just HAVE to have the reassurance.

I am not the original poster but the first reply to that OP. Yeah my car makes this sound for around 30 seconds then quiets. The car has 887 miles on it currently. My thoughts were the same on exhaust heating and expanding. I will most likely have the dealership look at it. I have had other new cars and they did not do that. My wife has a new Maxima with Sport pkg and it doesn't do the 30 rattle sound etc. It starts and the exhaust is quiet. period...

Spoke with service yesterday and they believe something is loose. I will have to schedule an appointment and take it in to service. Oh well we will see.

It is a brief rattle, every cold start - so maybe it's a little longer than 5 seconds but no more than 15.

It would be surprising that the rattle would go away due to heat expansion that quickly because nothing is even warm to the touch in 30 seconds of running at the muffler. But that's where the rattle sound is coming from.

@red6speed actually our WRX does make a cold start noise but comes from the engine and sounds more like valve chatter for a few seconds.

I would be curious if anyone with an aftermarket header-back exhaust reports the same sound.

[edit] saw Pats response. This has done it from new since day one of ownership - like I said it's more annoying sounding than anything but I am interested in figuring it out for sure. I'd be fine with the pre-heat logic.

My G37S did it as does my Z. Either that's one heck of a coincidence between two cars built 3+ years apart, or it's normal.

Mine does it as well (always has since new). It takes about 15 seconds to go away unless I put the transmission in D (and it goes away right away). Perhaps it's just at a particular RPM since the 6MT guys get it also? A cold start has a high RPM and it slows down after 10-15 seconds, putting the 7AT in gear also slows down the RPMs.

My car has always been rough initially as well, and it's been that way through a long series of exhaust changes (all factory, stillen headers + berk HFCs + factory CBE, stillen headers + berk HFCs + stillen CBE, stillen headers + berk HFCs + FI CBE, and now FI LTH + FI CBE).

With the very aggressive exhaust setup I have now, the initial "rattle" period actually rattles the loose hardware on my garage door, which makes it sound like a loose bolt on the car, but it's not on that car at all :). It's pretty insanely loud and vibrational.

But anyways, it used to make me nervous, and I'd go back and triple-check bolts all over the place. Never found anything loose. The engine's just really rough and rattle-y for the first few seconds when started dead cold, and it passes as the revs begin to drop from the ECU's cold-start process.