vibration, knocking standing water

[moisty]

On Friday drove 100 miles from Edinburgh to Lochgoilhead driving sensible as had a passenger that got travel sick easy. Weather was really bad and a lot of standing water and a few streams going across the roads. S3 8l AMK drove as normal with no issues.

Driving back myself I had a bit of fun for the 1st six miles on single track roads until I heard a really bad knock rattle that lasted maybe 20 seconds. At first I thought either exhaust had come loose or a spring came loose. Car then drove fine again as I tried to find a safe place to stop. I continued to drive home and the sound came back twice when going through a lot of water.

Since then car has drove perfect in dry,wet and slight snow.

I not scanned car yet but has anyone heard of anything similar? Seems like a few golf r drivers have experienced something like this but can't see a cause.


Sorry for the rant but any ideas what to look out for would be appreciated.

 

[wareham]

I have exactly the same thing but haven't found the problem so just here to find out I'm afraid.

Car drives absolutely fine until go through a puddle of water or heavy rain on the road resulting in loud vibration, exhaust sounds like its blowing and a knocking noise somewhere underneath the arm rest. Disappears within a few minutes, I don't even stop to pull over and check anymore as I've looked under the car that many times there's nothing visibly wrong. Although as the exhaust note gets louder I am swayed towards its the exhaust. The only thing I can think of is that going through water cools the exhaust where it joins and therefore contracts that ever so slight amount, blowing for a short period.

 

[Erikn89nl]

Water getting on the hot exhaust, causing the metal to rapidly cool and contract, potentially touching something?
Pretty sure I've heard that somewhere before... Are you using potentially worn engine mounts? Are the bushes in the dogbone uprated?

 

[GeorgieS3]

I have this exact same issue, not sure what is is. But as you described it comes from directly below the arm rest! Weird.

 

[moisty]

Thanks for the replies, sounds like we've all got the same problem but my exhaust note doesn't change. I've had the pink dogmount bush fitted approx 2 years but do wonder if my exhaust has moved slightly when going over the single track roads which isn't helping when exhaust cools.

 

[GeorgieS3]

It's strange that we've all got the same things happening. I'm sure last time mine did it, it felt like/sounded like induction noise got louder as well.

 

[Stuart B]

are you sure it is not misfiring with water on the electrics?

 

[LennyST8]

It's 100% you exhaust expanding and contracting due to the water cooling it down rapidly. Had it on my civic and now on my 8L, only after fitting a poly dog bone mount. Its because it moved it slightly, it's catching on the drive shaft I believe when it expands causing it to knock.
Anyway told my mechanic last week as it was in, he knew straight away, has adjusted it and should be sorted (not had it back yet)
Makes on hell of a bad noise when it happens.

 

[moisty]

Thanks, sounds exactly like what's happening to mine. Did notice yesterday a slight vibration from the exhaust when the car was ticking over, so will get exhaust adjusted.

It is a horrible sound to hear from you S3, you really think it's dying.