[mariojas]

So I checked videos of the famous exhaust rattle and mine sounds way different.
Mine has weird, like rattle sound, on low speeds, low RPMs, like 4th gear (M6) at 1.5 - 2k RPM. I hear it on the back of the car. Over all exhaust sound too "raspy" like tin can. Is this normal? Shall I save up for axle back maybe?
It's not picked up by camera very clearly, but here: https://youtube.com/shorts/O7iHurOkoMY

Another thing, which is also kind of weird - exhaust can be much louder at specific RPMs, like on-off switch when giving it a bit more "beans" than "chill cruise" (not too much, not gentle). It feels like sound is getting amplified, not gradually, but suddenly. Is this BOSE's "Active Sound Management"? https://automotive.bose.com/vehicles/chevrolet/camaro Because it kind of sounds like it could be related to the ANC, like switching from ANC to amplifying sound... Weird, if you ask me.

New ZL1, currently at around 800 miles, but both things are present since first test drive...

[Mac7504]

The exhaust getting louder is the npp opening isn't it? It closes when cruising in certain speeds/rpm from what I've read.

You could pull fuse 51 to see if it always sounds like what you're experiencing.

[mariojas]

Originally Posted by Mac7504

The exhaust getting louder is the npp opening isn't it? It closes when cruising in certain speeds/rpm from what I've read.

You could pull fuse 51 to see if it always sounds like what you're experiencing.

Yeah, I hear on idle huge difference when I turn on Sport mode. But there is weird zone above idle where it can be quiet'ish on Sport. But shouldn't valve be always opened the same way in Sport mode?

[Mac7504]

Originally Posted by mariojas

Yeah, I hear on idle huge difference when I turn on Sport mode. But there is weird zone above idle where it can be quiet'ish on Sport. But shouldn't valve be always opened the same way in Sport mode?

Nope. Even if you go into the exhaust setting and set track mode, it still closes. Some people pull the fuse to keep it open 100% all the time.

[mariojas]

Originally Posted by Mac7504

Nope. Even if you go into the exhaust setting and set track mode, it still closes. Some people pull the fuse to keep it open 100% all the time.

OK, I can believe in that.
Now the problem with the first thing. It kind of sounds like muffler goes into resonance or maybe valves? I will raise rea tomorrow maybe and see maybe there is something super obvious to fix...

[Mac7504]

Originally Posted by mariojas

OK, I can believe in that.
Now the problem with the first thing. It kind of sounds like muffler goes into resonance or maybe valves? I will raise rea tomorrow maybe and see maybe there is something super obvious to fix...

The first problem, it does sort of sound weird to me, mine doesn't sound like that. Sorry I can't help on that one.

[SATINSTEEL1LE]

Does sound weird. Mine doesnt sound like that and I have a new 21 ZL1.

[mariojas]

Sounds like new car needs a fix, ugh.

I just looked around, didn't see anything abnormal or rubbing. I took a wooden stick and tap-tap on the valves - one feels solid, second very much - I can hear tiny rattle in there, which maybe be much louder during above described conditions. I hate going to service for warranty fixes

[LT4Greg]

I really don’t think you have a issue as I did listen to the video clip and it sounds okay to me. My advice is put more miles on the car to see if the exhaust gets better(maybe the new parts in the exhaust) need more heat cycling from driving it. With just 800 miles your ZL1 hasn’t had enough time to break in the engine or other parts on the car.�� Good luck!

[arpad_m]

As stated above, sudden loudness changes are due to the NPP valves opening and closing, there are several rpm-specific tables that control the valve position. Fuse 51 is the fix if you want it loud all the time.

As to the rattle, I can't hear it in your video, but these are the potentially applicable TSBs. I performed them on my car, no NPP rattle since doing the second one.

16-NA-003
18-NA-172

I know these are older documents (I don't keep updating them, given I have a 2018), but I don't think gm changed anything about the exhaust since 2016/2017.

[mariojas]

Originally Posted by LT4Greg

I really don’t think you have a issue as I did listen to the video clip and it sounds okay to me. My advice is put more miles on the car to see if the exhaust gets better(maybe the new parts in the exhaust) need more heat cycling from driving it. With just 800 miles your ZL1 hasn’t had enough time to break in the engine or other parts on the car.�� Good luck!

Yeah, video gives like 20% of what I hear live. Please don't tell me it needs miles - you sound like salesman This is exhaust, something is loose, so only soot can fix that... But anyway, first available appointment is 11 days from today, so it will get some miles.

[mariojas]

Originally Posted by arpad_m

As stated above, sudden loudness changes are due to the NPP valves opening and closing, there are several rpm-specific tables that control the valve position. Fuse 51 is the fix if you want it loud all the time.

As to the rattle, I can't hear it in your video, but these are the potentially applicable TSBs. I performed them on my car, no NPP rattle since doing the second one.

16-NA-003
18-NA-172

I know these are older documents (I don't keep updating them, given I have a 2018), but I don't think gm changed anything about the exhaust since 2016/2017.

First one is not applicable - opening and closing valves is fine, some metal on metal noise but nothing to complain. Second one might be applicable, although I heard people's rattle and it was on idle - my car needs to get into some resonance in order to hear it. It's like you put two thin sheet metal pieces side by side and blow something on it... it kind of reminds me of beer can buzzing sound. Maybe I like beer too much

[LT4Greg]

Originally Posted by mariojas

Yeah, video gives like 20% of what I hear live. Please don't tell me it needs miles - you sound like salesman This is exhaust, something is loose, so only soot can fix that... But anyway, first available appointment is 11 days from today, so it will get some miles.

I wasn’t trying to sound like a salesman but going on my experience with cars over the years. Anyway good luck with your ZL1!

[mariojas]

Originally Posted by LT4Greg

I wasn’t trying to sound like a salesman but going on my experience with cars over the years. Anyway good luck with your ZL1!

I know

Another video, this time with tacho and speedo, so I am sure we are on the same page

It is getting so much louder at WOT, but I don't want to do that while driving with one hand.
I don't know, it sounds like beer can thick muffler walls, or it something is loose inside. Are you sure this is normal? I will try send this to technician before my appointment. If this is normal... then I am buying cat back...