Exhaust Exhaust resonance

[keel]

My catback was interfering with my rear sway bar when going over bumps and stuff (I have a Magnaflow system and it seems like this is a common issue with these) and so I cut it up and welded it for better clearance. The exhaust clears everything great now but in doing so it seems like I changed some of the acoustics.

I now get some nasty constructive interference at roughly 1800-2000 RPM that almost sounds like I dropped a cylinder or something, like a wavy, chopping/chugging sort of thing. Really sucks when I'm on the freeway since I'm sitting at that RPM range right at 75 MPH. Every other RPM is fine.

Anyone know how to smooth out the sound back to how it was originally?

 

[General karthief]

Got any pics of how this mod was done?

 

[keel]

I think the drivers side has a slightly longer tube after the mufflers.

 

[General karthief]

Nothin jumps out cept that dog bone.
I wonder if you got a pile of slag or a metal sliver inside the pipe that is in the flow of air that is causing the sound?
Wish I could hear it live and in color.

 

[2000xp8]

I've never seen the exhaust welded a second time under the frame right behind the muffler.
Could just be a vibration from that.
I'd say i've never heard of such a thing as the sway bar hitting the exhaust, but when i looked back, i posted in a thread about it, so did karthief, lol.

 

[alutwon]

in that last pic, are you positive it isn't hitting the rear frame rail as it vibrates?

 

[gkomo]

This isn't a open hole to the exhaust is it?

 

[keel]

in that last pic, are you positive it isn't hitting the rear frame rail as it vibrates?

I don't think so, the tube is held in there pretty good and I've had it hit the frame rail before and it's more of a clunk. For any of you musicians out there that have tuned instruments before, its like the "beat" of two pitches that are close to each other but not quite the same.

This isn't a open hole to the exhaust is it?

No, the ends are slip fit so they have slits cut in them for expansion. That gap you are seeing has a second tube underneath it that extends out of the muffler. I haven't seen any evidence of leaks but I may try clocking the exhaust clamps to see if that closes up anything I can't find.

Also hard to see in the pictures but the mufflers themselves do have some minor dents and stuff from me banging on them with a mallet when I was trying to take all this stuff apart. That could be a factor too.

 

[keel]

I've never seen the exhaust welded a second time under the frame right behind the muffler.
Could just be a vibration from that.
I'd say i've never heard of such a thing as the sway bar hitting the exhaust, but when i looked back, i posted in a thread about it, so did karthief, lol.

The Steeda rear sway bar I've got is much bigger than the stock one, I never had any issues with the stock sway bar. Yet another example of creating problems for myself by doing upgrades...

Are you talking about the weld that is on the bend going over the axle tube?

 

[2000xp8]

I'm referring to the one that is near the spring in picture two.

Maybe you know this, but also, to troubleshoot what is causing the noise (which i think it a vibration), you have to have the jackstands under the rear. The clearances change drastically when the rear is hanging.