I have recently reinstalled Cattman's catback exhaust. Had the stock exhaust on the car for Dyno purposes, and then bought a Magnaflow muffler to see the sound. I was not fond of the sound on my I35 and reinstalled Cattman's B Pipe, midpipe, and Muffler. Driving off the line, I noticed now that something sounds like it is hitting the floorboards on the car. I rechecked the tubing and hangers for the exhaust, but they look to be in place and stiff. It only happens off of the line under heavy throttle. I know Brooklyn has potholes and such but this happens under acceleration only. Even if I am in second gear and the auto downshifts, it still happens. sounds like something is hitting the boards or maybe the shocks are bad. Anyone have any answers as to what this could be? I have stock suspension on the car.

 

If the elbow on the muffler pipe isn't hitting the axle hole, then probably the b-pipe is hitting the bracket below it.

 

From what you described, its probably your b-pipe. Mine does the same thing accelerating and downshifting. In my case, its not the crossbrace under the b-pipe (mine is already removed), but you should check that first to see if that's it. If that isn't it, then its hitting a heat shield of sorts closer to the rear, which I can't describe fully right now but will try to get pics of soon when I try to fix it.

 

try checking in front of the rear axle towards the the middle of the car for any points at which your exhuast is hitting. I had to cut a cross beam due to my exhaust hitting it all the time.

 

i had the same issue of it clunking and it wasnt the cross member either. i just took it to a muffler shop and explained the problem, and he found took care of it in less than a couple of hours. he said in front of the rear axle somewhere it was hitting the floor boards, and they bent the pipe a little and added some spacers and was good to go. i know you probably want to do this yourself, but it was $75 well spent for me for a shop to do it.

take a look in the heat shield area like Joel said, but if its an actual clunking or something actually hitting, it isnt the heat shield because that is thin metal , it doesnt clunk. at that point your pipe is sitting too high and probably hitting the floorboards just before it bends like mine.

 

Thanks all. Good suggestions. I will take a look over the weekend and repost the problem. Its def not the heatsheild. The heatsheild is too thin to make a noise like this. It is clunking in between the driver and pass floor by the foot area. These things are so hard to diagnose without two people and it not happening until take off. I really didn't want the local mechanic sticking his head out of the car while we were moving..might run over his head. LOL Thanks again. I was wondering if it could be the suspension, but I raised the exhaust enough to clear both of the cross braces, maybe a little too much.

 

Oh by the way..its clcunking under the FRONT floorboards, not rear.

 

i felt mine under the front too. i dont know if it was reverberations or what, but i could feel it under my feet and almost in the pedals too.

 

I guess I misspoke because I have 2 separate issues. My b-pipe is clunking and is making contact with something right before it bends, just like you described. However, my muffler is rubbing on the heatshield out back as well and squeaking like a ****, that I know for sure. I'm busting out my grinder this weekend.

Regardless, since Sleeper's problem is towards the front, this doesn't even apply.

 

Yeah, it's tough to diagnose rubbing or clunking under the car, especially when it only happens under acceleration. I didn't have much time to spend at the shop, and they hate me by now anyways because I have been there 100+ times doing various things. If the bay isn't taken, it's only because I wasn't around that day! I will see what it is over the weekend.

 

i just wasnt paying attention fully to your post

 

now that i read your post Joel, i get it.

it is hard to pinpoint something, since just because you feel it under your feet doesnt mean its actually happening under there. the vibration travels thru the car and at least in the maxima, thanks to the absolute 0% sound deadening in there, it can travel a long way. like i said mine was hitting in the rear and i consistently felt it up front.