New headers in, but what's this???
 

I recently had LT headers/cat/xpipe installed. Now I have a wicked resonance/vibration/buzz that goes through the whole car (and eardrums) at about 3500 rpms. I've had a Borla Quad cat back for a couple years, and never had any resonance problem. Anyone ever experience this? I still have the stock cat-back. Maybe I'll try to swap it back to see if it goes away. :bigears

What headers?

Check to be sure you have clearance from other structures from the headers all the way back to your mufflers, sounds like the pipes are buzzing against something.

:iagree:

I double checked the clearance on a lift. No contact anywhere. It's a very professional installation. I don't want to name the header yet, beause I'm sure the installer will correct the problem. If it can't /won't be fixed, I'll elaborate. I was hoping someone had seen this and had a fix.

Possible something out of whack in a collector?

With stock cat back you should not be hearing resonance like that. With stock cat backs even with headers and no cats it should sound fairly quiet with no resonance.

Sounds like the system is loose, but you said you checked it. This is a strange one. I have heard of the internals on cats coming loose and causing noise but that is usually a rattle or clicking sound.

It really does sound like it is setting against something or loose.

Double check your clearance. Especially the passenger side where it goes over the axle. I had something similar and the pipe was touching the differential. There is not much room there at all.

Is it from outside the car or inside?
I have a wild buzzing noise in the passenger compartment at that RPM after I installed my headers. It is coming from the driver side, rear speaker grill/trim/assembly.

Had the same exact problem with my C4 after installing headers, and a new Corsa Catback with Random Tech mini cats.

After speaking with one of the techs at Corsa, I was informed that there was a reason why Corsa placed the resonators where they are on an unmodified system. And that is, to remove the resonance which occurs at that precise spot in the pipes.....some sort of mathematical formula that's beyond my feeble mind is used to arrive at that conclusion.

After explaining just what I had for an exhaust system and the exact measurements of where each component was located, he suggested that the Random Tech mini cats be moved downstream such and such a distance, and after having done so, the nasty WOT resonance at 3500 rpm virtually disappeared.

Just for what it's worth. :cheers:

If you installed high flow Cats then that is your problem. I had the exact same problem when I installed my headers. Went back to the stock Cats and the problem went away.

:iagree: I had this happen to me, minor adjusting and all was fine. Are your connections welded together?? If not, the clamps may be the cause also. Good luck :cheers:

At 3500 mrpm, the engine torques a little on the mounts. Maybe the torque causes parts to come into contact. Just a SWAG...

The problem does appear to be in the cats. When you tap on the right side cat there is an obvious tinny sound, like something broken internally. (Sort of sounds like a metallic snare drum) We're going to check it out next week. Thanks for all the responses. It's also throwing numerous HO2S codes for all four sensors. Have to double check all wiring, etc.

Make sure your 02 sensors aren't hitting the tunnel plate. Clearance there can be very tight.

It may be the cat, but that may only be a secondary symptom. If you have some sort of contact somewhere (could be lots of places) and vibrations are being transmitted to the cat causing it to fail, replacing the cat will only get you so far. Keep an eye out for witness marks at places where the exhaust is close to things and could potentially be in contact as the driveline moves.