I installed Crawford cats on my car about a month ago. They sound completly normal when accelerating. Whenever I engine brake and it hits 4 grand I get this buzz noise. It's just for a second, but it's loud and sounds like crap. It pretty much did it as soon as they were installed. I checked all the bolts and nothing is loose and nothing was rubbing. Anyone else have this problem or any idea what it may be?

 

were they brand new? i know when your cats are getting bad from the gas they start rattleing. other than that not sure

 

Yes, they are new. They were doing it as soon as they were installed.

 

Perhaps your HFC is making contact against the heat shield when
the engine is under heave load.
Mine did this badly in the beginning, but after I bent the
heatshield in, it dissappeared.
My crawfords are off at the moment since both sides cracked,
but my car now has weird vibration and buzzing when the engines
on moderate to heave loads around 3-4k RPM.
I've tried different HFC afterwards, but the buzzing is still there.
Maybe something's loose, or it's simply the exhaust itself that's having a problem, but it's still bothering me.

 

I thought it may be the heatsheilds as well. The were rubbing so I took them out completly and it has still been doing it. I really like the sound of the cats but the buzzing sounds like crap.

 

you need to check again because it does sound like a rattling problem...even if you checked the problem when the car was cool, the heat and/or driving can possibly cause the cat to shift back to the spot where it is rattling

another thing is COULD be is a leak, but judging from the fact that it happens around 4k rpm only it sounds more like a rattling problem that i used ot have with my test pipes

 

You're describing exactly what I had when I had the Kinetix HFC's and then again when I decided to try Helix non-resonated TP's. Nasty, ugly hissing/rattling noise. Sounds like absolute GARBAGE, it was the only reason I took the HFC / TP off my car, because other than that, the gains up top were nice, but I couldn't handle that sound!

 

I'm running non-res. test pipes & I hear rattling at times as well. It's really noticeable when I cut the ignition; it sort of makes the car sound cheap (not solidly built). Could it be the heat shield? It almost sounds like something is loose (like a bolt).


I also get the annoying hissing sound. You can hear it hissing off and on when the motor is idling but it's really pronounced when I lift my foot off the throttle-it almost sounds like a subtle blow-off valve or something.

 

it's rasp.

 

If you hear a rattle with our cats, 99% of the time its the heat shields (either on the car or on the cat rubbing something. It is not a big deal at all to bend either shield to cure the rattle. It sometimes does not cause a problem until it warms and cools a few times.

The throttle let off hiss / air rush sound is just that . . . alot of it has to do with your complete exhaust system (headers, cats, y-pipe, mid-pipe, muffler). Having run several styles of cats, I can understand the annoyance of certain sounds. After running gutted high flow cats, I was ready to go back to stock cats for the peace and quiet. I instead opted for the high flow cats with the new design brackets. So far so good, and back to an acceptable noise level.

 

I took the heat sheilds out and it still does it. I still have the stock cat back.

 

bump..i have the same problem..im switching back to stock so hopefully it fixes the situation..im willing to try anything to get rid of that damn rattle/buzzing

 

Let me know if it helps

 

What you are hearing is an inherent problem with running fairly open exhausts on the VQ. I know exactly what sound you're talking about. It sounds like a very distance rattle of a bolt in a coffee can. The truth is isn't a loose shield, cat brick, whatever. What you're hearing is a nasty trait of the VQ firing order. GM's 3800 series V6 makes a somewhat similiar sound, even with a stock exhaust.

 

I agree I had a camero with the 3800 series engine in it and with high flow or gutted cats, it sounded just as you are saying.

 

I had the same problem with my Crawford Hi Flow Cats a while back. If what you are describing is VERY loud then you might have a broken bracket. I had mine re-welded and I don't have that rattle anymore. I still get buzzing sounds ocassionally with my set up but there's really nothing you can do about that.

 

I'll jump on board here as well. When leaving off the gas i'll get the rattlesnake at about 2500 rpm's. Screw it. I checked everything, the tp's are tight.

 

That's good to know. I was just worried that something was wrong with them. It realy does sound like crap. Sometimes it's worse than others.

I checked it all again when I changed my oil. It all looks good. No cracks and everythings tight.

 

maybe next time you are underneath the car, grab the pipes and shake them... probably be easier if u step and shake, up down left right back and forth, maybe its not he pipes rattling but installing them made something else rattle, worth a try... i can't stand noises that aren't suppposed to be there

are you sure the sound when you cut off the engine is from the pipes? i get some noise too but its my tranny, doesn't make a sound when i clutch while turning the car off

 

No, it is only when i engine brake. It only does it at 4k rpms. It never did it untill right when I put the high flow cats on.