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I have an 04 civic sedan with an APEXI N-1 catback exhaust.And when it rains for some weird reason it starts shaking(the whole cat back). when it dry outside its just fine.Its fine for a while driving in the rain but then after a while it will starts to shake off and on also i can feel my automatic shifter start to rattle .I took it back to the shop that installed it,and they were puzzled they never had that come up before.they put my car on the lift and took off the whole piping and it was just fine but then they saw that it was rubbing against heat sheild under where the backseat is.and bolted the piece back in place.And put everything back on.and told me to come back if it still does it. Then in the afternoon it shook some more in the rain.i kinda think water getting in through the intake but its short ram.Does any one else have this problem?Because i want to get this fixed cause im really not trying to let this car go. thanks

 
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If you look around the forum you will find a lot of people have similar problems in the rain with aftermarket exhaust systems. The tolerences of the civic leave little room for the piping to move. Whe the exhaust system gets hot from running and rain water splashes up onto it differnt portions, the piping cool whereas other portions remain hot. This result is the pipe deflecting/deforming slightly. It is ususally enough for the exhaust to come into contact with sway bars, the frame, and other components underneath. The solution is to determine where it is making contact and either modify the pipe in that area or use high temprature insulation to protect the part that it is bumping into.

As for your second comment. I don't believe any water is getting in your intake.If any water did manage to make its way into the intake the motor would not be happy since water is (by definition) incompressable and could blow the motor if it entered the cylinders. Hope this helps you out a bit. I am sure there are plenty more people here who will have more specific information. Good Luck!

 
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much appreciated bro,has anyone else had this problem?all the help i can get will be appreciated. thanks

 
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My civic did it as well. Its annoying as hell, but doesnt cause any damage.

 
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yup, annoying. I just deal with it ! Greddy Evo 2

 
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i have a greddy evo 1 with the same exact problem on my 02 ex. i'm getting the same kinda noise underneath my front passenger seat. i took it to the shop just as you did and they told me to find a muffler shop and ask them to lower the piping a little bit. it is worse in the rain, but now, after having my exhaust for 2 years, it happens all the time. for some reason, 90% of the time, it happens when i turn right. anybody else have the problem? i hate the noise, it's so annoying so i'll be getting fixed.

 
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Thanks everyone,and earlier i failed to mention that when it does this, i rev my car afew times and itll stop the noise but a little later it starts.Really not trying to get a new exhaust cuz apexi has one of the best piping out there.Once again thanks for your input

 
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DC Sports TCS... Same problem as yours..

 
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1) it is a common problem
2) it is from the lack of flexibility in an aftermarket exhaust
3) nothing you can really do unless you get 3 pipes and move it, so i suggest learning to live with it

 
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same problem here, when that tropical storm from Dennis came through my town, i was rattling against my car and shifter. then when it dried up, no problem. but i dont drive much in rain, if i can not at all! but Magnaflow cat-back does it too! but o welp! i deal with it. it sounds better now than it did b4 i took off a welded hanger the Muff shop installed on it.