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S18 RSG

What could the noise be?

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As some of you may have seen, I recently purchased a 1320 UEL manifold, which was subsequently fitted today. Upon fitment, my mechanic said that the car was making a whistling noise. He took the manifold off, resealed everything, did 3 leak tests, smoke tests and everything else, and found no issues, but the whistle was still there.

I arrived to pick the car up, and heard what, to me, sounded like the signature fuel pump chirp at idle, which went away and was replaced with the boxer burble under load. During revving, there was some slight rasp, which could be categorised as a whistle I suppose, but nothing that sounded too dramatic (at least to my ear).

Now of course, the car as it stands is no longer fitted with a cat, so despite being loud, I would imagine that a slight rasp to the exhaust note is normal, and therefore refitting the secondary cat should help reduce that, but after having the mechanic and my dad both explicitly refer to this 'whistle', I'm trying to figure out what it could be, especially given that an exhaust leak has been checked for multiple times, and all shuts sealed with exhaust paste and gaskets.

Anyone have a similar experience, or failing that just some idea as to what is likely to be the cause of this?

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No intake leaks checked, but to be honest if there was an intake leak, it would have been heard before the manifold fitting. Both mechanic and dad said it's only there since.

Leak checks were done on hot exhaust as he had to warm it up to get some heat in the bolts to remove them.

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Would that be likely to be heard at idle or partial throttle? This noise is more obvious, now I've spent a bit more time with it, under 25% or more throttle. It's got the rumble of UEL headers, but it's almost being masked by this whistle.

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I'll try that in the morning Church. When I got home I tried having a proper listen, it sounds like it's coming from the manifold for sure, just can't quite pinpoint it.

I wonder whether there may be something silly like paper jammed in there. That's the kind of noise it makes, but then it's only heard under 25% or more throttle. Under gentle revs there is no noise. It's strange.

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OK, I have a small update, hoping that someone can chime in with an idea from this video I recorded this morning. You will need to listen carefully, as the video didn't pick the noise up too clearly, but it can definitely be heard, and is louder than it seems when driving.

Going to tag @Mark@Abbey M/S in this too, as he knows the car and may have seen/heard similar before.

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2 minutes ago, rob275 said:

Nothing sounds odd to me

That was my fear, the video really hasn't picked it up well at all. I think it's most obvious, in that video, when I come off throttle. There's still that slight high pitched tinny whistle.

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I can hear a slight noise at the end when you blip the throttle a bit but difficult to tell if it's something or just the noise from the throttle being blipped a few times. 

What about attaching a camera outside and recording?

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9 minutes ago, Deacon said:

I can hear a slight noise at the end when you blip the throttle a bit but difficult to tell if it's something or just the noise from the throttle being blipped a few times. 

What about attaching a camera outside and recording?

I'll attach the GoPro later, and take a few clips from under the bonnet. I'll also see if I can find my Rode mic and record in car with that, might pick it up better.

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Since changing my manifold Ive got some strange sounds too, I can hear a 'Wooshing' sound, quite annoying, but mines only under throttle! Seen similar things on US forum saying its thinner sidewalls of the manifold producing the noise! 

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3 minutes ago, Tom B said:

Since changing my manifold Ive got some strange sounds too, I can hear a 'Wooshing' sound, quite annoying, but mines only under throttle! Seen similar things on US forum saying its thinner sidewalls of the manifold producing the noise! 

Mine's only under throttle too, anything over 25% or so pressure and it can be heard. I hope putting my secondary cat back in might quieten it down, but I'm not getting it refitted until Monday, so looking for any other issues in the meantime, in case that doesn't fix it.

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I think I can hear it, and mine does the same if it's what I'm thinking it is. I think it might be resonance in the manifold tubing.

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4 minutes ago, Rich said:

I think I can hear it, and mine does the same if it's what I'm thinking it is. I think it might be resonance in the manifold tubing.

I'm glad you saw this, and especially that yours is the same. Are you full catless, or secondary cat in place? I've read that wrapping the manifold can really help, as it's mostly down to the thin metal as Tom mentioned (I looked up that same thread just now)

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Secondary cat is in place. If anything it was more noticeable with the stock catback (probably as there is less noise to drown it out).

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With mine I'm sure I can feel a banging/knocking from the front end slightly since having my manifold/over pipe fitted. Can't hear anything, just feel it. Not sure if that's resonance either but gonna pop the covers off later just to check everything is good :) 

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12 minutes ago, STEVO9000 said:

With mine I'm sure I can feel a banging/knocking from the front end slightly since having my manifold/over pipe fitted. Can't hear anything, just feel it. Not sure if that's resonance either but gonna pop the covers off later just to check everything is good :) 

when I had fitted my JDL UEL I was getting similar to what you describe, turns out it was rubbing on the undertray so just reshaped the area where it was rubbing so no longer came into contact and no more noise

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3 hours ago, Tareim said:

when I had fitted my JDL UEL I was getting similar to what you describe, turns out it was rubbing on the undertray so just reshaped the area where it was rubbing so no longer came into contact and no more noise

 

Awesome! I shall have a look at that if the rain decided to stop :) 

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Yeah can easily hear it here too, a high pitched whistling, maybe something to do with the air intake, unsure by just seeing the vid

Try removing the air filter and see if it changes

I'll give that a go, cheers Mark.

I've booked the car in to the garage that fitted the manifold so he can fit the stock cat back in place on Saturday (I never really wanted to go full catless anyway). I'll hang around and have a listen under the car and see if I can identify it better.

I'm also going to order some heat wrap. If it's true that the thin metal is a cause of this noise, surely a good quality wrap will help deaden some of that noise, and of course keeps under bonnet temps down.

On that note, anyone got any recommendations for a good quality wrap, along with a guess of how much I'll need?

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