fvckbg

wassup guys. A couple months ago installed a new cat back exhaust and it ran really good. No problems at all. I think it was made by spec D. Then just yesterday I installed a new catalytic converter (v tech) and my car sounded great. I can tell the difference in horsepower. But now when ever I press the gas hard I hear this rattling noise. It begins from 20 mph and it stops when it shifts gears them starts again but when I'm going like 65 or above it runs smooth. What's the problem? I looked it up and i saw answers that said "change octane fuel" or something like that. Or a loose hanger. Idk Also have a 98 civic ex

GolNat

iTrader: (7)

Probably a rattling exhaust/heat shield.

Lift car and look.

old97civic

Yes most likely rattling heat shield. Some of mine were removed quite some time ago, but just this past June I was leaving a parking lot and heard some rattling. I replaced the muffler in Oct 2013, so I was surprised to hear the sound and thought maybe some baffles inside came loose. I had a look to make sure nothing was actually dragging on the ground. Once I got home I saw that it was the heat shield above the rear section of pipe where it turns from the middle toward the passenger side. The tab at one end of the shield broke off but was still holding on by 2 bolts at the other end, so the shield was swinging up and down banging on the pipe. Bolts were not accessible due to the pipe, so I drilled a couple of small holes through the shield and used some wire to tie it to the frame. Plenty of places to tie off to.

Wankenstein

In the following statements I am not trying to be a nit-picking *****..just seeking (or describing) clarifications:

Your post is somewhat confusing. Is the car you are referring to a 1998 Civic EX or do you also have a 1998 Civic EX ?
If the car you're referring to in your post is an EX it already has a catback exhaust from the factory (unless a previous owner modified it). Not sure what a Vtec catalytic convertor is so I'm assuming you mean a high-flow cat. You are most likely getting 0 power gains and you really wouldn't know unless you did a before and after dyno.. what you are possibly experiencing is better shifts and a deeper exhaust tone.

As mentioned previously it's most likely a rattling heat shield or you may have forgotten to tighten down exhaust bracket nuts

fvckbg

I found out what it was. At least I think I do. I think it's the muffler vibrating a lot which is hitting the area that surrounds the muffler because I adjusted the hangers and now the noise isnt as loud as it was before.