Hello guys and gals. I just installed headers and cats to complement the intake and exhaust on my Z. All in all I have the Nismo CAI, Headers, and Exhaust along with the Crawford Hi Flow Cats. I'm very happy with the results and everything seems to be working out ok EXCEPT that sometimes I get this LOUD vibration/groaning sound coming from under the vehicle. I don't think it's what you guys describe as rasp as it only happens sometimes and under certain situations. I hear it after I lift my foot from the throttle and the rpm's start to slowly come down. I know there should be an increase in noise from the exhaust when I do this but this particular sound is different. I don't think it's a rattle between 2 pieces of material as everything seems to be hooked up pretty tightly down there. However, I can't be sure as it seems to be more pronounced when i'm travelling over bumpy surfaces. BUT sometimes it ALSO happens over flat areas. It seems to be coming from within the pipes themselves. It's almost like a loud groaning sound that sounds different from what I consider 'normal'. Can you guys try and explain what that might be? Is this normal for my setup? I don't know if I should take it to the dealer to have it checked out or not. I believe I read a thread once about some of the gases running back up the pipes and causing a louder buzzing sound. Hopefully there's nothing wrong with my car and it's just me freaking out. Any input would be greatly appreciated. Thanks!

 

whats up i don't have the same exhaust or anything as you but i did have a vibrating noise every once in a while under deceleration coming from under my car. it turned out to be coming from some black piece of metal that is bolted on under the car, some kind of air deflector or something? there was one on each side near the center of the car. i pulled it down and let go real quick and it produced a similar sound as it vibrated... so i drilled one drill-bit screw through it and into the frame for each so that it wouldn't vibrate when i pulled on it...problem solved...don't know if it's the same sound your describing though or not

 

You know, I also noticed those black deflectors and thought that they might be the problem because everything else seems to be bolted on pretty tightly. I'll have to fasten them down better like you did and see if that is the problem. Process of elimination I guess. Thanks for the info.

 

This is the drone you get with the Nismo exhaust & Crawford cats. I get the same thing. Mine is pretty loud at around 2500 RPM's. I'll also get it when I take my foot of the gas after accelerating or if I just touch the gas lightly. I don't get any drone over 3000 RPM's. Something you will have to live with to get that sweet sound at WOT.

 

I also get it at around 2.85k-3k rpm. I guess i'll just have to get used to it. I don't mind it as much as long as I know that it's normal. It just sounds so different than what it usually sounds like at any other rpm. I guess it is normal then and I should just get used to it. I will take a look at those deflectors that 350zwarz mentioned. Thanks for the input. Anyone else?!

 

I can't hear any drone

tilton, 3.9 final drive, headers, cams etc cover it all up or seem to change the sound where I don't consider it drone, but maybe some of you do consider it drone.

I consider it just hearing sound come out the rear of the car instead of just the front