I’ve searched the forums on this topic with no definitive solution to the problem. There’s a lot of speculation about what causes the HFC rattle & hiss. Some even report they have no rattle & hiss. I can live with the hiss, but not the rattle. So what’s really going on here.
OK, let us assume that all exhaust bolts are tightened to spec and there are no exhaust gasket leaks. Also, refrain from suggesting replacing Berk HFC and 350Z HR Y-pipe with Motordyne ART pipes and XYZ pipe. I know they are top notch, but my intent was a less costly exhaust replacement since my mine was severely rusted from spending some time up north. Now, let us find an inexpensive solution.
This what I found so far. Please Chime In with Your findings. What have you tried, what worked, what did not work.
Here’s a link to a pic of the underside of 350z for reference (close enough).
http://liljerk.morpheus.net/350Z/images/zbottom.jpg
SYMPTOMS:
Rattle comes from engine ( HFC ) area under hard acceleration. 4K rpm and higher.
No rattle under no load rev.
SOLUTIONS:
Replace exhaust hangers.
Remove Heat shield or adjust bolts to Heat shield on muffler.
Remove the offending heat shield or bend away from exhaust..
Higher octane gas.
Install a Stillen engine damper.
Replace worn engine mounts.
Add washers to the W shaped chassis brace for more exhaust clearance.
Add weight to Berk HFC to simulate weight of OEM cat. (Via the aftermarket exhaust fix method).
Add a damper to Berk HFC. See this link called “aftermarket exhaust fix method” http://forums.freshalloy.com/showthread.php?t=198141
Heat wrap Berk HFC & Y-pipe.
Replace with another coupe mid-pipe. Bad resonator.
Use magnaflow 11385 or 14385 X pipe.
Remove “hockey puck “ dampers from 350Z HR Y-pipe.
Get a tune.
Something loose inside the Berk HFC. Replace.

 

I was thinking of heat wrapping my HFC's and X-pipe portion. Don't know if it's safe, effect performance or get rid of/silence the hissing and rattling...

 

I had the same hiss issue when I was running Berk HFCs and the HR y-pipe.
I swapped out the HR for the Tanabe y-pipe, larger diameter.
It got rid of a lot of the hiss, but I can still hear it on deceleration.
It also helped to diminish the rasp as well.

Oh yeah, I'm running the Tanabe Medallion exhaust.

 

I'm running Berks hfc's and ARK cbe. Only rasps/rattles during cold starts or when the hfc is cold. Hisses during deceleration too.
But when everything is warmed up rasps/rattles goes away and the exhaust sounds amazing but the hissing remains but tones down.
I really want to heat wrap the hfc and x-pipe portion but I wanted feedback from someone that has already done this too..
Maybe we'll be the first?

 

No solutions yet. We are working on a HFC as well.

 

the hiss is definitely present on the deceleration when you have the factory exhaust!! I cant wait to upgrade to an aftermarket cbe

 

Reduce Berk HFC rasp with resonator<!-- google_ad_section_end -->

<HR style="BACKGROUND-COLOR: #606060; COLOR: #606060" SIZE=1><!-- / icon and title --><!-- message --><!-- google_ad_section_start -->As some of you know, the addition of Berk HFC's to a stock exhaust can cause rasp, rattle and hiss noises.

First, have your exhaust system checked for leaks by an experienced tech. Gaskets should also being replaced if needed. Also make sure that exhaust components are not making contact with any of a number of heat shields. Make sure exhaust hangers are in good condition and that the exhaust system is properly aligned.

My setup: '03 coupe 5AT with JWT pop charger + Stillen air box + 5/16 Motordyne plenum spacer + Z tube + Berk HFC + 350Z HR Y-pipe + 4x22" resonator + OEM muffler

After installing the Berks with the HR y-pipe the exhaust had a deeper tone at idle. However, under load at about 3000rpms there was an horrible raspy rattling sound that drove me crazy. I was about to remove the Berks because that rasp was embarassing. While searching the forums I saw a post by DaveB describing "a metallic pinging/faint clank with some rasp under load from 2800-3500rpm's ... most often incorrectly diagnosed as a loose or broken internal exhaust part"

DaveB suggested replacing the OEM resonator or "center muffler" as described in the service manual with a larger one.

Magnaflow manufactures a glasspack model # 18146 about 30" long which is probably too long for G35 coupe but it's good reference . The resonator is a straight tube that is preforated and packed with some material that cancels certain exhaust tones. The one I used was generic, a round glasspack 4x22" from a muffler shop installed for $60. I think 22-24" will be the longest you can use without a sharp bend in exhaust tubing.

The new resonator removed about 90-95% of the rasp even at 5500rpm. The exhaust note is probably more quiet than stock at idle. Under load, the sound is nice. I can hear the sound of intake again and the muffler exhaust note still sounds like a G35.<!-- google_ad_section_end -->

BTW, the hiss is still present. Could the OEM muffler be the culprit?.

 

^ I can't seem to find the inlet/outlet diameter sizes for the oem muffler.
What's the diameter of the Magnaflow?
Basically any smaller diameter piping past the Berk HFCs (2.5") will increase hiss.
Just depends on the degree of diff.

 

I have Kinetix HFC version 2, HR Y pipe, coupe mid pipe and 05-06 sedan muffler. I have the hiss, only when the revs drop down. I also have the metalic rattle around 3k rpms. Its seems to go from 2800-3800 rpms. How do I fix?

I'm thinking about trying a new resonator in place of the coupe midpipe and maybe a magnaflow muffler or vibrant muffler.

 

I installed my BERK'S HFCs to my HKS HP exhaust system with new OE gaskets and have zero issues with hiss or rasp. Apparently installing BERK'S to the OE exhaust even with an aftermarket y-pipe causes issues. Rattles are caused by the pipe coming in close contact with anything on the undercarriage. That can be resolved by getting your ride on a rack and following the system from front to back making sure you have enough clearance thru out. (crowbar)
Gary

 

Berk HFC, MD XYZ w/resonator and OEM exhaust, no rasp. Love the deep sound but I do get a slight hiss at about 2500 rpms on decceleration. Sounds like a pressure release to me but it's so slight I can only hear it when i'm in my garage and warming up (??) because it's gone by the time I return home.