I have myself a J's Racing decat pipe which I put on when I installed my Buddy Club exhaust a few weeks ago.

I've had to take the exhaust off as it's too loud for the track day at Donington tomorrow. Since putting the OEM exhaust back on I'm getting a buzzing noise around 5-6000 rpm when I lift off.

It sounds like it's coming from the centre of the exhaust system and I'm wondering if the noise is coming from where the decat meets the manifold. I got the below "ring" with my decat, but I'm not sure if it's meant to go in between the decat and manifold or between the decat and exhaust.

Any ideas?



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There is a donut that sits in the joint on the downpipe. Acts like a ball joint.
It allows the de-cat to move about (hence the spring loaded bolts).

There should be a gasket between the decat and the exhaust. This looks like it could be that gasket.

Are the bolts done up super tight?

 

I've got a bvrand new oem donut gasket

 

Bibbs - This circle gasket won't fit between the three bolts between the exhaust and decat, besides I already have a gasket there anyway, so I'm happy it doesn't go there.

I'm trying to fit it between the manifold downpipe and decat but I don't think it's meant to go there, as I can see that donut gasket you mentioned.

Maybe I didn't tighten up thos etwo spring bolts enough.

 

That flat gasket goes from decat to exhaust, if anywhere.

It looks like it sits in a recess, I think an OEM one has bot holes in it?

Assuming you haven't disturbed the manifold to decat joint in taking the BC exhaust off, and ot wasn't noisy before, then surely it must be the exhaust to decat which is the issue?

But if you already have gaskets in both ends then it might just be a bolting issue.

Take the bolts out, get the alignemtn right then evenly bolt it back up.

 

I've taken the above gasket out from between the manifold and de cat as I couldn't do the spring laoded bolts up with it in. I loosened off the three bolts between exhaust and decat and did up the two between manifold and decat. Then went back and did up the rear three.

I've just tried it again and the buzzing is still there.

No idea what it could be

The only other thing to try is re fit the cat and see if the noise is still there. I don't think anything is going to break, but it would be nice to know what's causing it.

 

Well there must be an unsecure metal to metal contanct somewhere...

If it was all fine until you took the BC off, then its got to be something to with the OEM to decat joint.

 

With a bit of luck my old man came home for lunch and with me under the car and him rev'ing the nuts off it I'm 100% sure the noise is not coming from the connections on the exhaust system around the decat pipe area. It sounds more like it's coming from the rear driverside of the car.

I'm wondering if one of the baffles in the OEM exhaust has become dislodged when I was taking it on/off?

 

Hmm, could well be if its coming from that far back.

Did you try gripping it in place to see if it improved or stayed the same?

Its pretty well held in place so doubt its touching anything...

 

I checked all round the exhaust and it's not touching anything, and like you said it's held in place very well with those five hangers.

As it's some kind of resonance noise it might not be the exhaust, it could be something else which makes a noise when the rev gets up to 6k rpm.

I did think it was that protective plate which attachs to the lower rear arm bar (which I took off when I re fitted the OEM exhaust), but I can't see it moving and all those bolts are torqued up.

I'm going to re fit the Buddy Club on Sunday (weather permitting) and if the noise goes away (fingers crossed), it must be something on/in the OEM exhaust.