Exhaust, CAT or something else knocking?

[dansonamission]

Fitted new exhaust yesterday, CAT Back, custom job, all was ok apart from it was blowin slightly on the joint to the CAT. Ive sort this out today but now something is making a knocking noise. Its almost like theres something in the CAT.

Some time when its idling it does it. Sounds quite metalic.

Handbrake on, 4th gear bring up the clutch so engine bogs down, it rattles.

and some times when goin round small ish round abouts it does it.

Any ideas any one?

 

[gaz44]

CAT maybe broken up inside?

 

[dansonamission]

My center section on my std exhaust was making a right noise at 4K rpm, hense the new exhaust.

I had been driving around last night with it blowing and no knocking noises. Its only started making a noise since i fixed that. Would the pressure in the exhaust now be anything to do with it and broken the cat down like you've mentioned?

 

[Da]

knackered mount?

 

[dansonamission]

which mount?

 

[Peperami]

Sounds like the exhaust bend just before the back box is hitting your rear axle as it passes over it fella.

Check how much clearance you have between the two...

 

[Da]

Sounds like the exhaust bend just before the back box is hitting your rear axle as it passes over it fella.

Check how much clearance you have between the two...

agreed, check the rear mount at the backbox.

 

[dansonamission]

back box is fine, its all one piece.

Just been out again, its really bad when its cold, it even does it doin 30mph in 3rd or 4th. Go above 3 to 4k rpm and it goes.

Couldn't get it to do it this time with handbrake on in 4th.

Oh what does exhaust sealer smell like when its hot?

 

[Peperami]

So is it a knocking noise or a metallic rattle, bit like a buzz saw?

 

[deviltronics]

could be the the exhaust manifold/cat flanges hitting the top of the steering rack heat shield. just bend the heatshield out the way.

mine did it, but only when driving hard, not at idle.

more of a knocking noise.

 

[dansonamission]

its a combi of knocking noise and a metallic rattle.

more metallic rattle.

 

[Peperami]

When changing your exhaust over, they've disturbed the heatshield?

They sheer through where theyre bolted quite easily, guessing if it only happens at 4k revs its this.

 

[dansonamission]

Over about 3k revs its not there, its when the car is idling cold and some times when its hot.

when driving at about 30mph (cold) it does it too.

Cant get it to rattle when i boot it.

Its a random sound, its not consistant like a vibration

 

[Da]

Have you checked the clamp at the CAT on the exhaust side? Is it definitely not blowing anymore?

 

[dansonamission]

Its definatly not blowing any more.

iirc the clamps are all ok, i will jack it up tomorrow and see if i can see any thing wrong.

damn cars, one thing after another!

 

[Peperami]

Check the bolts that hold the heat shielding are all in place too fella.

 

[Da]

Who fitted the exhaust, was it DIY or Pro?

*edit* is this the '4k rattle'?

 

[dansonamission]

will do. I think it makes the most noise when you start the engine. Just dont understand why its doing now ive sorted the blowing out GRRR lol

 

[mini-valver]

Did you say you've exhaust puttied it? If so, it's probably come loose from the exhaust and rattling around on it.

 

[dansonamission]

It was covered in exhaust sealer stuff, not quite sure what it was.

 

[mini-valver]

If

 

[Da]

Check the clamp springs that fasten the cat to the downpipe as these can look tight but in reality be loose.

 

[mini-valver]

If it's the stuff I'm thinking of, it goes rock hard and if it's come away form the exhaust it rattkes around on top of it like buggery

 

[dansonamission]

Theres nothing on top of the exhaust or the CAT.

Is it possible some of this sealer could be inside the cat? The noise was noticed about a minute after first start after adding the sealer. I was told it goes hard in seconds once hot, plus exhaust was hot to touch whilst i unbolted the exhaust and added a gasket and sealer.

 

[dansonamission]

I think the noise is too violent to be exhaust sealer rattling around.

 

[mini-valver]

I mean, the paste is put around the exhaust, if it comes away it will rattle around on the pipe. As if a metal ring were hanging around it, see what I mean? Could of gone into the cat yeah, seperate the center section/cat and have a look.....

 

[dansonamission]

Ive got to the bottom of this now. The second lambda sensor is knocking against the heatshield. Its made its own dent on the edge of the heatshield and now i rarely hear the knocking noise.

The exhaust must be slightly off alignment compared to before when it was blowing.