I'm having the same problem!! I completely removed my heat shields. But something still rattles/vibrates when the car warms up. Is there any other shied to look at? My noise comes from the rear passenger side.

 

My heat shields are failing too. Both sides have the spot welds gone.

My fix was to go under the car and take a wire coat hanger, wrap it around and tighten it up with pliers. This fixed 95% of the rattle/buzz under load, but once in a while I still hear it from the driver's side.

Guess i need another coat hanger.

Very annoying, but i'm not replacing the entire pipe.

 

I just started having a similar issue over the weekend.
I started the car and it sounded like rod knock. I gave it a bit of gas to see if the noise would increase with engine revs, it did increase a bit, but after a certain(higher) rpm it went away. When the rpms came back down the noise came back. I went for a drive and the noise would come and go. It seems to have gone away at a steady speed/rpm when on the freeway. This morning I started up the car and it seemed worse, but every once in awhile it would go away and then after about 15 min of driving it went away completely.
We never drove over anything to bend the heat shields, so I dont know how the noise would come up all of a sudden. Im going to jack up the car when I get home, I hope it something simple.

 

Due you have any lose in power it could be one of your cats when they go bad they start to crumble. It sounds like rocks in the exhaust and when they get really bad you will notice a lose in power and the bad cat will run hotter than normal because of the blockage of the honey comb falling apart inside the cats preventing the exhaust gases from going out the tail pipe.

 

You don't have to hit them to have them fail. They rust over time and the welds fail.

Right under where the drivers and passengers feet are the heat shields. Give them a tap with a metal rod and see if they rattle a bit.

 

Your not crazy. When i test drove the first g35 i heard it and walked away from the car. It happens in mine also. Usually when i first turn it on. Not even fully cold. but i get the rasp also.

 

Interesting you say that because I recently got a smog check done on the car and I had the weirdest outcome. Everything was perfect for 15mph across the board (barely registered anything!), and everything was perfect for 25mph but the very last # which was for NO, it was close to failing. Usually if the car is going to fail, it would be in the 15mph range. I'm wondering if there is something blocking the cat now. When I get home Im going to check the cat/shields.

 

I was going to say heat shields... every single Nissan I've ever owned has had the problem.
Glad to see removing did nothing (well, sort of ... I guess your wasted effort at least helps one dude out


Someone mentioned the flex pipe - can anyone confirm? I have the same problem.

 

My flex pipe is starting to show "tearing". I don't feel any leaks when someone revs up though. Right now, i think I'm dealing with heat shield rattle...which is annoying as hell.

Hope i don't need to track down a Y-pipe used and swap it out to fix the issue.

 

Anyone know anything about the universal cats from magnaflow? I don't believe they are hi flow cats either. Spotted them on eBay.