I don't know if anyone has experienced this noise that i am having. It has been there since the headers were installed. When i am coming to a stop and the truck is downshifting, there is a little vibration, like in any truck, and something rattles, it's hard to explain. I attempted to fix the problem a while ago and thought it was fixed, but turned out not. I had my dad put my truck in gear and power break it, just a little to get the exhaust to vibrate, and i went underneath to try and hear it, i saw the driver side CAT rattling, so i hit it with a rubber mallet, and got it to reproduce the noise i had been hears. PROBLEM FIXED, SO I THOUGHT. Called dynatech, paid like $170 for a new driver side pipe w/ new cat, replaced it, sent the old one back, got my money back. Drove around for a while, sounded perfect. Did a hanger and shackle kit on my rear, drivline vibrated like a mother, the noise returned. Put a Carrier Bearing relocation bracket on, the noise got better, but still there. It's even worse when i come to an emergency stop and the truck downshift quicker at the end, and when going over any really bumpy roads and slowing down at the same time, it's real bad. IT's the cat/cats rattling for some reason. I go in and all the frickin bolts are tight. I am think i should just order the off-road y-pipe, put that it for now, and then when it comes time for smog, just put back in my catted pipes. What do you guys think? What is rattling, i am almost certain it's the cats, all the signs lead up to it. I have HPT so i can eliminate the rear 02's, but what about the front two, what happens if i do go catless, what do i do with the 02's?

 

Mine had a vibration for a while on the passenger side. Turned out i had a bolt that was barely touching the frame and it would make a loud vibration. I ended up pulling the bolt and cutting almost 3/4 of it off and then putting it back in. Now no more vibrations.

 

When I put my Dynatechs on, it took a little work to get the y-pipe in a good position so that it would clear the transmission support, heat shield on the transmission, etc. I think I ended up moving the locaion of the Y by pushing the passenger side cat someone off-center and toward the frame. You should be able to get the Y-pipe section to clear everything, including the heat shield on the transmission. But if it does all fit ok and you still hear a rattle, also check the header itself. On my 5.3L, it is a little close to the frame. Hopefully yours has plenty of room.

Also on your headers, is your front passenger side spark plug wire boot real close to or up against the header? If so, did you do anything to prevent it?

 

Check on the exhaust hanger behind the y closest to the frame. I had a vibration exactly like the one you are talking about....I found that the hanger was making contact with the frame, a little chop chop of the hanger (about 1/2 inch) and it has been quiet since.

Remember that not all aftermarket manufactures get together and make sure all of their parts work together, if you have an aftermarket cat back, I am willing to bet that the hanger in the rear is the issue. IF needed I will take some pics in a few days for you.

 

I do have a cat back, that could be the problem. I am going to check everything you guys mentioned this weekend. Blownchevy, if i need pics i'll let you know, i appreciate it.

 

On my Dynatech system the large flange after the y-pipe to the cat-back was only about a 1/4" or less from the frame rail causing a rattle, that was audible at slow speeds and going over bumps. I could always swear when in the truck it was coming from the drivers side but it wasn't. The instant I put the truck on a lift with it running, I said damn that's an easy fix.

 

I looked at the whole exhaust today. Looks to me like the Passenger side header is hitting the frame, it's like 1/16 of an inch away from it, that can't be right. Is anyone else's that close on the passenger side? I looked through everything, and can't simulater the noise, i move the whole cat-back exhaust and nothing is hitting, it's gotta be the actual header.

 

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Mine had a problem on the 90* bend of the piece you replaced. It would vibrate against the transmission crossmember mount. I did some adjusting (as mentioned earlier) and grinding (frame mount and the weld at the bend). Everything is fine now.

Here are some pictures showing some clearances and my problem, before and after.

 

Same issue with my SW longtubes. They hit the frame in that same location during left turns.