Loud knocking during the wet only...

[ItWasntMe]

As the title says, I am getting a really loud knocking noise coming from under the rear/middle of the car, only during heavy rain and driving through a fair bit of standing water. Literally, I have driven for miles and miles and the noise will not occur.

As soon as I hit rain/puddles, I will sporadically get a very loud (almost akin to when my Astra GSi had 3 people in, and the exhaust used to knock on the rear axle as it looped over) knocking noise. Arch liners are fine, suspension is supposedly fine and the exhaust is nowhere near (and OEM) any other parts of the rear axle or chassis.

Please help me work out what this could be?

Leejw has been out in it, looked under it, around it, and he is stumped (he's not God or anything, but he knows more than me!). He had no idea what it could be, neither did SVA Imports when I took it down to them. A heatshield was removed from underneath, but to no avail.

Thanks in advance.

PS It will sometimes make one or two solitary knocks of a similar (can't say it's identical) nature when I'm reversing, or sometimes over a bump in the dry, but only the one knock.

Cheers.

Phil

 

[cup_66]

Could be if you have an aftermarket exhaust,the water can cause this to happen..i suffer from the same problem!

 

[leejw87]

I thought this noise Stopped when SVA replaced the o/s/r Shock Absorber?

Im sure the reverse knock your probably getting is something different as this noise only happens when you drive through standing water.

I think we should take it for another drive when wet and maybe try swapping your wheels around as cheap or unevenly worn tyres can make funny noises.

either way its a very strange sound that only seems apparent when driving through a puddle :xconfused:


Ps and i am GOD !!! xdevilking

 

[ItWasntMe]

Could be if you have an aftermarket exhaust,the water can cause this to happen..i suffer from the same problem!

Thanks for the suggestion, but its a standard exhaust etc.

And it just stopped after they did the shock because its hardly rained since!

 

[buckley 88]

When I had my Mongoose cat back on my ep3 type r, every time I went through a puddle I would have a huge knocking, vibrating sound coming from the bottom of the car, could feel it through the seat aswell!!! stumped me for a few weeks, then realised it was the water hitting the hot b-pipe (making it bend) and striking the chassis of the car, a common fault with the exhaust apparently.

 

[ItWasntMe]

it was the water hitting the hot b-pipe (making it bend) and striking the chassis of the car, a common fault with the exhaust apparently.

Thanks! This sounds like the noise I'm experiencing. Is there any known way to fix it at all?

 

[Coldfuse]

i wouldn't have thought that the exhaust would be made hot enough to bend..... needs to be alot hotter than the engine can make it, especially if its being cooled by rain water. have you had the car up on stands to get a proper look at it?
If its just when you hit a puddle it would suggest that either its litrally the water making the noise or its the water pushing something to make the noise. Id need to take a look before i could tell you anything more... by no means an expert either.

 

[raz786]

Ad mentioned earlier in the thread, water hitting the b-pipe, especially on buddy club exhausts from past threads, causes a very loud vibration, but when I experienced it you could feel the whole vibration go through you and the seat. Unless it's like this it may not be the b-pipe.

 

[ItWasntMe]

Ad mentioned earlier in the thread, water hitting the b-pipe, especially on buddy club exhausts from past threads, causes a very loud vibration, but when I experienced it you could feel the whole vibration go through you and the seat. Unless it's like this it may not be the b-pipe.

You can hear and feel the knock all the way along the middle of the car. It's been up on ramps and nothing looks out of the ordinary. Really annoying me now as this s**t weather is continuing.

I reckon it's the B-Pipe after hearing what you've said, although it is all OEM under there. Leejw thinks it could be the tyres... I really don't think it is though as the knocking is quite violent - any takers on that one?

Any help in solving this will result in much gratitude and beers.

Thanks,

Phil

 

[Stylesa]

As said, its the b-pipe. on mine, its very close to the underside of the car at the flange beside the edge of the manifold (directly under the seats)... when you drive through and the exhaust is warm, it will cause the metal to expand and contract, and the natural vibrations of the engine will cause the exhaust to bang on the under side of the car right under your seat.... mine was quite violent too. Nothing to worry about.

It no longer does it now that i installed stiffer engine mounts.

good excuse for you to buy engine mounts.... :wink:

 

[raz786]

B-pipe seems to be the majority view, are there any marks on the underside if the car to show if the exhaust is knocking it?

 

[leejw87]

B-pipe seems to be the majority view, are there any marks on the underside if the car to show if the exhaust is knocking it?

The B Pipe has been grounded out at some point in its life and is sitting pretty close to the floor pan and has marks on the underside already so this could be the cause

the noise i heard sounded more of a rumble when going through standing water which would point to tyres to me as the ones that are on the car are very cheap lol

i think phil is getting new ones soon so we will see if this has any effect on the noise. if not than i would opt for a B pipe as the one thats on there is bent from it being grounded out.

 

[ItWasntMe]

Right Lee well as soon as it rains hard I'm coming round and we're going puddle hunting!

the noise i heard sounded more of a rumble

To be fair, that may have been my stomach!

the ones that are on the car are very cheap

And I'll have you know, Autogrip are a well known brand! They come as standard on Hotwheels and Matchbox cars!

 

[PooM]

OMG! I thought it was just me!

I have had this problem since I have had the car! I have had an OEM exhaust and I now have a Fujibitsu RM-01A cat back. Whenever I go through standing water, it sounds like my exhaust has fallen off, vibrations and sounds like it's blowing! Then after 30secs of driving the noise gradually goes away. I have had it in the air a couple of times and nothing out of the ordinary is showing..mmmmmm

What could it be peeps?

 

[Paul G]

OMG! I thought it was just me!

I have had this problem since I have had the car! I have had an OEM exhaust and I now have a Fujibitsu RM-01A cat back. Whenever I go through standing water, it sounds like my exhaust has fallen off, vibrations and sounds like it's blowing! Then after 30secs of driving the noise gradually goes away. I have had it in the air a couple of times and nothing out of the ordinary is showing..mmmmmm

What could it be peeps?

Had this on my car when racing at Silverstone in the VERY wet, came in because i thought the exhaust was falling off. Turned out to be just metal to metal contact from the rear box mountings, just push a bit of fuel pipe onto the hanger that was catching and no more prob....

Like has been said, only ever happened in the wet...

 

[PooM]

Had this on my car when racing at Silverstone in the VERY wet, came in because i thought the exhaust was falling off. Turned out to be just metal to metal contact from the rear box mountings, just push a bit of fuel pipe onto the hanger that was catching and no more prob....

Like has been said, only ever happened in the wet...

I find this very odd that this only happens in the wet? Why would water make your exhaust sit any different to make metal to metal contact? :S

 

[ItWasntMe]

I find this very odd that this only happens in the wet? Why would water make your exhaust sit any different to make metal to metal contact?

That's what I've been wondering! I actually can't believe it's only when I go through standing water, but it is.

I may get an occasional knock when going over some bumpy road, but nothing like the knocking I get when I hit a puddle.

Iirc, it's something to do with water hitting the pipe and making it expand or something? But I don't really get it either. Is there anyway to fix/stop it without getting a new B-Pipe?

 

[buckley 88]

As said, its the b-pipe. on mine, its very close to the underside of the car at the flange beside the edge of the manifold (directly under the seats)... when you drive through and the exhaust is warm, it will cause the metal to expand and contract, and the natural vibrations of the engine will cause the exhaust to bang on the under side of the car right under your seat.... mine was quite violent too. Nothing to worry about.

It no longer does it now that i installed stiffer engine mounts.

good excuse for you to buy engine mounts.... :wink:

Spot on, this is what happend to my civic, only way to fix the fault is to somehow lower the brackets to get some more clearence between the b pipe and underside of car

 

[ItWasntMe]

Changing to a de-cat stopped this noise completely. Will be putting a new manifold on this weekend and hope the noise doesn't return. But it definately stopped when I took the cat off!

 

[Real R]

I hate to bump this tread but i been going crazy trying to figure out wtf is happening to my itr... Got the car back in January and it didnt rain that much until last week..


So i took a drive the other day and got caught in a heavy shower after about 20 mins the car started to shake and man i was scared, so i booked the car for an inspection at our local performance shop and guess what they came back with NOTHING!!!

I didnt know where else to turn but here, man its a really wierd problem.. any possible updates on a fix?