Last week Victor, Smitdog and I installed a Mugen 4-1, SMSP Carsound Cat, and Fujitsubo RM-01A exhaust on my R.

A week later I have been noticing a rattle that appears at 2500 - 3100 rpm under load. This rattle does not occur in neutral or when the car is not moving. It only occurs in gear and in motion. I notice it the most in 2nd - 5th gear. The sound appears to come from the area where the header meets the catalyst. Doesn't sound like its coming from the rear muffler section.

I put the car on a lift today at a muffler shop with two techs and they noticed nothing obvious. We knocked all the exhaust pipes and the cat converter with our fists. Everything was solid. No sounds of loose honeycomb in the cat converter. The muffler hanger was solid too. The heat shield was not touching the exhaust at all.

Any ideas? Why does this sound only occur when in motion and in gear? Could it be the heatshield?

 

Most likely could be the heatshield, although its not touching, the heatshields may be closer to the exhaust than stock, and at a certain resonance or vibration, may make contact. I had the same problem when i put my carsound cat... it was 1/4 inches too long and because it pushed the exhaust back slightly, caused a bunch of contacts, both near the catalytic and where the rear b-pipe bends.

 

I'm thinking heatshield as well.

 

Agreed on heat shields. ALso check the O2 sensor contacting or very close to the shifter bar (I have this problem with my Carsound). Do a search, heat shield rattle is well documented. Also check for loose or mis-aligned cat flange bolts.

 

Or maybe it's touching the sway bar.

 

OK so after installing a $69 header from ebay I got the rattle.. As a DIY guy I wanted to install the thing myswelf but rusted bolts and time constraints let me to a local shop... After I got it back I had the rattle... This morning I went back and they were not open (even though the web site lists Saturday hours) at any rate... As I looked down from the top of the engine to where the fron motor mount is, directly to the right is the 4-2-1 connection very close to the cross member the motor mount is bolted. THat cross member has now got a small channel cut out of it to allow for the header pipes and the gap is less than .25 inches... Given that motor mounts flex and this has very limited room I am going to try to cut this out a little more and see if it fixes my problem... I will let you know what I find as I am going through the rest of this thing piece by peice... FYI I am doing this on a 2001 Accord 2.3

 

Seriously?

 

Yes seriously. Once I suspected this area I sat on a level parking lot with the e-brake on and waited for it to come back. Then I opined the hood and sure enough the pipe was touching the cross member just slightly. I got some channel locks and bent more metal from the cross member lip row and away from the header. No more rattle problem solved.