Has anyone else had anthing like this:
when i drive my car @ highway speed in heavy to moderate rain, the exhaust gets loud and not in a good way, also it sounds +/- feels like the exhaust is rattling/rubbing. If the rain lightens up or i pull off and slow down it return to normal....I have no idea what it is, its been doing for years (w/ 3 diferent rear sections).

I have, stillen Y + 2.5 SS B pipe + OEM style replacement rear section. I have been under the car, and from the Y to the tips, the exhaust has plenty of clearance, I have shook the hell out the exhaust I realy have to make an effort- rocking it side to side, to have it contact anything. I have left the car reving @ 4K rpm and sprayed down the exhaust w/ a hose from engine to muffler and on more than one occasion, can never get it to repeat. I am lost, I suspect it may be the flex section, b/c it is a bit old and worn, but i have no explanation why it would do this.

any sugestion, anyone else have this...and fix it

 

I am inclined to think whatever you are hearing is not your exhaust... It just makes no sense.

Are all splash guards in place/attached correct?

 

this noise is defiantly coming from exhaust, it is difficult to localize "where" it gets louder since I am in the car driving when it happens, but the rubbing/vibrating seems to be coming from below and to my rear and gets worse when i rev up the engine (as does the exhaust noise).

for a while i though it may have had something to do w/ the intake (injen knockoff), like perhapses it was sucking in a small amount of water, or the filter got wet and severly restricted the intake. I shortened my intake and the filter is now high and dry.....no effect

 

make sure you have no exhaust leaks. when my stock exhaust started leaking, it made this huge vibration that you could even feel though the floor at high speeds.

 

The flex sectionis a little rattly, some of the SS braid is fraying but not leaking and the rest is tight. I had a new rear section put on last winter, and the shop welded some tiny cracks on my Y and catalytic conv before they started leaking..... i jacked it up and took a good look today (before i tried the spaying w/ the hose again) and its solid

 

do you still have your cross-members on near the cat and rear section?

After I put on my aftermarket exhaust, the exhaust would rub on them making a vibration... Only thing I can really think of, but I don't know why it would only be a problem in the rain...

 

It was half on in the rear, so i finished the job and ripped it off yesterday. Of all the things the ehaust runs near that had the least clearance, but it wasnt tight.......i guess i will see if that had anything to do w/ it tonight - forcast calls for heavy rain in boston

 

Interesting, I actually have the exact same issue. Throttle sensitive rattling and vibrations from the exhaust both in the rear of the car and sometimes right under the center console, and only in the rain/wet. I first encountered this two weeks ago on a drive from VA to DE in the rain, and then again this morning on a short drive to the subway station. I've looked under the car and found nothing loose or broken.

 

sounds like water/moisture some how is changing the tones and noises you typically hear in dry weather.

Could it be the H2O making the metal exhaust piping moist and hence the different noises?
IE. stock mufflers have holes in them to let out water that actuall gets trapped inside the muffler?

 

OK, so i am not alone. we have the same problem. what is your exhaust setup?

we can eliminate the cross member as a source, I now have none on my car and there is no change.....its raining in Boston and on the way home today i made every effort to hit standing water/puddles. Ran through plenty w/ the drivers side, w/ no effect but after i drove through a good one w/ the passenger side there it was.

Increased (throttle sensitive) noise level,that seems to originate from 2 locations:
-under the drivers seat / center console
-rear passenger side ...around the muffler

the noise seems to have to components
-increased sound level of exhaust tone
-a rattling / rumble: as if a portion of the exhaust is in direct contact and vibrating against some part of the chassis.

Also there is clunking/banging of exhaust against some part of chassis when going over large bumps. It is particularly bad with wheel hop (never occurs when car is dry)

- all issues resolve shortly after i pull over, slow down or rain lightens up...(when exhaust dries up)

since i have some nice rain out there, i am going to don a garbage bag poncho and drive around hitting puddles to provoke the noise, then pull over and get on my belly as quick as possible to see if i cant get a better idea of whats going on underneath

 

That would be fun to watch...

 

On a more serious note...

When i first put on my ehaust i had a rattle problem... usually over the rear axle. It was always worse in the rain. I took it into the muffler shop had them heat it up and bend it a bit to give a little more clearance and the rattle has never come back...

 

yea, by the time i got out on the road, the rain had slowed then stopped. And there i was: wearing a garbage bag, on the the congested rush hour roads of Boston, driving erratically trying to hit any puddle i could. but the roads were not wet enough and i could not get it to act up......after a 1/2hr I said F**** it, i got a $1.00 hot fudge Sunday from mcDonalds and headed home.

there is likley an issue with the exhaust hitting something when wet, I figure some adjusting will be in order once i nail down where contact is being made. But i am not sure if that is the whole problem. On my way home from work today when it was raining heavy, i went through a puddle and the exhaust acted up. I immediately pulled into a parking lot, hopped out of the car and took a look under the drivers seat area (best i could w/o the poncho). Once out of the car, i gave it a rev and could hear a noticeable increase in the exhausts volume level, (like a sizable exhaust leak) that was coming from either the flex section or CAT. This was separate from the rattle coming from the rear.

my current working theory is; when the hot exhaust is splashed and cooled in one or a few places, by water kicking up from tires, its shape is distorted causing a leak up front and rubbing in the rear.

next heavy rain, i'm suiting up in the poncho, to see if i can better localize the noises .

 

Have you tried spraying the exhaust with a hose?

 

Have you tried reading?

That's from the very first post...

 

do you by chance use stock exhaust hangars?

 

I have an all stock set-up and sometimes have this problem. What would be the obvious thing to look for? Can I take it to a local nissan dealership and have it fixed? Or should I somehow do some spraying at 4k?

 

i think when i had this problem there was vibration on the axle back. the bend that is connected to the muffler would hit the metal piece that it's trying to wrap over. don't know how exactly to describe it.

im not sure if this is the exact same problem that you are refering to, but give it a look?

 

Sometimes my Greddy SP2 with hit the straps holding up the fuel tank near the rear axle on my 4th gen. Trying look there for the source of the rattling.

 

I am reading this as a result of a search.99 SE 5 speed Only in the rain and only after 15 -20minutes I get a rattling/spark knock noise under part throttle acceleration as push the gas pedal down. However it is only the middle range of the gas pedal travel. Once the pedal is past half way the noise stops. This never happens when dry and it doesn't set a code pending or hard. The exhaust is stock altough it appears the previous owner had the muffler replaced or taken off and reinstalled as there is a weld just before the muffler. Thanks

 

You guys sure the running thru water isn't affecting the heatsheilds location. I would check your heat sheilds to make sure all their hardware is still intact and the sheilds are secure! The run thru the water could be pushing the sheild down on the exhaust more like an airfoil effect and once you are thru the water it moves back to it's original position...As long as you have no exhaust leaks and all your hangar mounts are in good condition your exhaust should be the same wet or dry! UNLESS something else is being forced onto the exhaust by the force of the water! Hey, if you do have some weak hangar mounts go to NAPA theirs are just as beefy as NISMO for a cheaper price....

 

I wondered at first if it was the plastic splash guards at the front of the car - but I don't think so - The first time I heard it was in a serious cross wind and in the rain. What confuses me is the part throttle =yes / full throttle =no with regards to noise(I can accelerate thru it). Also I used to describe this as sounding like a dull matt knife trying to cut corrigated cardboard - hard to describe but you would know what I am talking about if you had ever heard it.

To further define part throttle - the amount you might use as you transition from the flat to an incline i.e. it doesn't take a lot of change in the throttle psoition for it to start and again only in the wet - I beleieve the road surface has to be damp so the idle that water is getting to location that that would normally be dry is a given. I never experienced this under full throttle.

 

Not the splash sheilds, if you were respond to post# 21, but the heat sheilds mounted above the exhaust systems bolted to the belly of our vehicles

 

I think you have loose main cat material. The sudden contraction of the cat as it cools dislodges the loose material and it floats around creating the knocking noise. The rumbling noise is probably due to less sound deadening.

 

I would expect the material moving around in the cat to not be rpm sensitive -I get the noise at light throttle under load. Once I get past a certain point(physical throttle position) it goes away. It is not setting a code and the mil light doesn't come on so I am going to live with it for the time being.

 

i've had exact same problem last year.

i'd get a nasty vibrating sound in the rain, and only in the rain.

i never figured the problem, but it went away when i replaced my whole exhaust with cattman y-pipe, test pipe, and cattman cat-back.