I just installed my exhaust today (RSR GT2) headers, test pipes, y pipe, and catback. As the car revs the exhaust sounds amazing but when you let go of gas, a sort of hissing or air leaking noise comes up. Its not a leak b/c we double checked that but what i did realize was that the Y-pipe flex pipes would vibrate majorly when you let go of the gas and that's where the noise seems to be coming from. Anyone know what can solve this issue.
I was thinking either give the flex pipes some time to flex if that makes sense, or might have to get a better y pipe. (mine is just regular factory direct from Statik Performance)

 

Could be broken flex pipes

 

Well they're brand new from statik. Although i read up and seen that this is quite a common issue. Bad thing is there's no solution yet. It has something to do with back pressure and it is caused mostly by the test pipes. Still, i think there is a solution. I was thinking test pipes with resonators and flex pipes and if needed a new good brand y-pipe. Im going to by some exhaust wrap in the mean time to see if wrapping the y-pipe might absorb the vibration and reduce the noise. Any suggestions?

 

Backfire? Do you hear something similar to this in this video?

Watch at 0:32 and 0:39 for a crackling noise.

My exhaust got my G35 did that too. Its normal, and is not backfire. Its just the way the aftermarket exhaust alters the back pressure. The stock exhaust is designed to provide certain back pressure/flow.

 

ya i hear it- its like that but i could say a bit louder. Best words to describe noise would be "rattle snake". It sucks b/c if you're driving down a road and u let the gas go a bit (lets say in 4th gear) all you hear is that sh***. If you check it should happen between 1500-2200 rpm.

 

And by the way, yours sounds like its coming from the tips but i know for fact mine comes from the y pipe.

 

Do you have a manual?

On my evo, anytime I'm in gear and let off the gas I hear a metallic like grinding noise coming from right underneath. But if I put even an ounce of throttle or push in the clutch, it goes away. Some people are saying its normal for an evo, or it could be just something vibrating against something.

Could it be that what you're hearing has something to do with the clutch/drivetrain rather than your exhaust?

 

Rasp from the test pipes

 

The reason why when you put in neutral the noise goes away because there is no longer air flowing through exhaust (well barely). And when you tip gas it changes the air flow which changes back pressure. I have manual so ya, i know exactly what you mean.

 

Rasp from test pipes is one thing which is usually heard more inside the car than outside- this though is 100% y-pipe that's shaking and flex pipes on it are the ones making the rattle snake noise.

 

i take back the neutral (gear) comment. Whenever it decel and goes through 2200-1500 rpm, the noise will come but tapping the gas just a bit will get rid of noise right away.

 

Could be an exhaust leak up front (or at the flex pipe or gaskets behind the flex pipe) letting in fresh air and allowing afterburn. If you can fix the hissing in the front you may fix the popping at the back.

Some amount of popping is normal, if it is annoying you it is probably not normal.

 

For the leak what i plan on doing is putting seafoam in vacuum line and then lifting car and checking if white smoke comes out any place other than tips. The backfire is cool tho, i like it. Its like the more u do to your car, the more annoying it gets to drive.

 

same thing happen to me. I got a hks hi power setup and when i had stock cats on it did not do it. The next day i got test pipes bam it happened right away. I thought it was a leak so my buddy and I took it apart put on new gaskets bam same thing.

 

i have test pipes and I know how the rasp sounds like from test pipes + stock exhaust, and test pipes + after market. Few months back after several times of scrapping my car, my Y pipe is massively leaking and I am having the same problem as OP. It mainly sounds bad when I let go of throttle. I know it's not the test pipes because the sounds are night and day different. I can actually feel the leak right underneath the flex pipes.