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For a while now I've had a rattling cat on the passenger side. I suspected there wasn't much left of either cat and now that the misfire and everything else engine related seemed to be sorted I had a new set of cats fitted today, so now have a full stainless exhaust (as I had a stainless cat back install last year when the back boxes started to give up). However it has now highlighted the rattle/tick noise that has been there for a while, but now that everything else is quieter, it's more obvious. I also blamed some of the noise on the rattling cats.
The exhaust shop also mentioned it today, as he said he couldn't hear anything from above/with the bonnet shut, but whilst he was underneath it was pretty noisy at idle. He said he's never really heard a noise quite like it before though and certainly can't point to what it could be.

He's right, it's difficult to hear in an open space with the bonnet shut, unless you bend down. It can be heard from either the drivers or passenger side if you get down low, but a bit more pronounced on the passenger side.
It's there at idle and can be heard at low speeds under acceleration if the passenger window is fully open. If the drivers window is open and passenger shut though, it's almost impossible to hear, which makes me think it's coming from the passenger side somewhere. With the bonnet open and head in the engine bay, it can be heard, but no way near as much as if you get your head down behind the front passenger wheel.

I'm convinced it's become louder than it was a couple of weeks ago, as it's hard to ignore now.

I've tried to capture it on video - this is with the camera held behind the passenger front wheel, reaching inwards. It's the slightly higher ticking/rattling noise that can be heard over the deeper exhaust noise. It is there from cold and will still be there after the engine is fully warmed up. It's also there in park and neutral too.
Video Link

Any ideas where I should start to investigate?

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have you changed the exhaust manifold?
you might have a slight blow on the gasket

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I can't tell you what it is but mine sounds just the same. It was like it when I bought it, it was the same 80k miles later after the engine was rebuilt and it still sounds the same after the gearbox was replaced. I replaced the cam followers as it seemed to be more cam speed than engine speed and that made no difference. When I first took the car to V8Developments before the rebuild, they couldn't work out what it was either but assumed that it would go away after the rebuild but it didn't. It has always been there has never got any better or worse so I just live with it although it is much more noticeable at idle. The Ascot also does it but to a lesser degree.

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karlos01 wrote:

have you changed the exhaust manifold?
you might have a slight blow on the gasket

I installed refurbished heads and head gaskets a few months ago, so all gaskets were replaced at the time. Originally, before I noticed the rattling cats, I thought this might have been a minor split or something in the exhaust manifold. It does sometimes sound quite like an exhaust blow, but then I can't decide, as I feel like it comes from lower down than that and if it was the manifold then I would hear it louder under the bonnet.

Honestly the closest place I feel like I could point the noise as coming from was the passenger side cat, so now it isn't the cat, I'm not really sure where else to look!

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Check the end of your dip stick for witness marks. Give it a curve so it bends towards the outer edge of the sump. I’m not saying it is your issue, but I have seen in the past a noise no one could find that was finally tracked down to a crankshaft balance weight brushing the end of the dip stick.

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Gilbertd wrote:

I can't tell you what it is but mine sounds just the same. It was like it when I bought it, it was the same 80k miles later after the engine was rebuilt and it still sounds the same after the gearbox was replaced. I replaced the cam followers as it seemed to be more cam speed than engine speed and that made no difference. When I first took the car to V8Developments before the rebuild, they couldn't work out what it was either but assumed that it would go away after the rebuild but it didn't. It has always been there has never got any better or worse so I just live with it although it is much more noticeable at idle. The Ascot also does it but to a lesser degree.

Interesting... I guess it's a little reassuring to know you have a similar noise, can't locate it either and you've had it for so many miles!
It really always sounded like it was coming from exactly where the passenger side cat was.
The exhaust shop guy said it sounds like the sump (he also said it makes it sound like a diesel from underneath :/ ). However I had the sump off the other month during the rebuild and it all looked fine in there, rather clean.
Yup at idle I really notice it, especially when parking to the side of the house on my driveway, as the sound echos off the wall.

Does yours sound like it mostly comes from the passenger side too?

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Marshall8hp wrote:

Check the end of your dip stick for witness marks. Give it a curve so it bends towards the outer edge of the sump. I’m not saying it is your issue, but I have seen in the past a noise no one could find that was finally tracked down to a crankshaft balance weight brushing the end of the dip stick.

Hmmm, interesting... Now that would make a lot of sense. It's only on the passenger side and low enough down...
I've never noticed any marks on the dipstick before, but it's worth a check tomorrow!

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I think this sounds similar to mine which I also can't find the source of. See the videos on my thread. Do you think they sound similar?

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jacckk wrote:

I think this sounds similar to mine which I also can't find the source of. See the videos on my thread. Do you think they sound similar?

I hadn't seen your thread until now, that's very similar sounding! Especially the video underneath.
Now I'm really starting to lean back towards the exhaust manifold... Is it as noticable from in the engine bay as underneath for you? And is it mostly on one side (looks like drivers side for your first video)?

I really don't think it's the rods or tappets etc, as I replaced my camshaft and tappets recently and it made no difference to the sound. The top of the engine also sounds rather quiet. I'm almost certain it's fairly low down, I just can't pinpoint the exact location though, even after laying under the car a while back.

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ac6 wrote:

karlos01 wrote:

have you changed the exhaust manifold?
you might have a slight blow on the gasket

I installed refurbished heads and head gaskets a few months ago, so all gaskets were replaced at the time. Originally, before I noticed the rattling cats, I thought this might have been a minor split or something in the exhaust manifold. It does sometimes sound quite like an exhaust blow, but then I can't decide, as I feel like it comes from lower down than that and if it was the manifold then I would hear it louder under the bonnet.

Honestly the closest place I feel like I could point the noise as coming from was the passenger side cat, so now it isn't the cat, I'm not really sure where else to look!

mine had a blow on exhaust manifold on passenger side(mines the l320 4.2 V8 supercharger) and could hear it more behind the wheel than under the bonnet just give the manifold bolts a little torque to make sure they tight enough

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karlos01 wrote:

ac6 wrote:

karlos01 wrote:

have you changed the exhaust manifold?
you might have a slight blow on the gasket

I installed refurbished heads and head gaskets a few months ago, so all gaskets were replaced at the time. Originally, before I noticed the rattling cats, I thought this might have been a minor split or something in the exhaust manifold. It does sometimes sound quite like an exhaust blow, but then I can't decide, as I feel like it comes from lower down than that and if it was the manifold then I would hear it louder under the bonnet.

Honestly the closest place I feel like I could point the noise as coming from was the passenger side cat, so now it isn't the cat, I'm not really sure where else to look!

mine had a blow on exhaust manifold on passenger side(mines the l320 4.2 V8 supercharger) and could hear it more behind the wheel than under the bonnet just give the manifold bolts a little torque to make sure they tight enough

It's worth a check, everything was torqued to spec at the time as far as I can remember, but the passenger side is easy enough to get to, to double check!

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always worth a check mate 👍

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Worth a check but I doubt it is a manifold blow. Manifold blow will be barely audible at idle, unless it is really bad, and louder when the engine is working harder, not the other way round. It, and the noise I have from mine, both sound more mechanical. In fact mine sounds loudest coming from the bellhousing but after the gearbox, including the torque converter and flex plate, were changed it's still there. About the only thing left that hasn't been changed or rebuilt, is the flywheel.

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Dear All,
Mine sounds the same, on a 10,000 mile Turner engineering engine. Always has. I've always assumed it was a stuck l;ifter but numerous oil changes and flushes no change. Comes from the L bank, ran it with rocker cover off all seemed in order. So no idea but reassuring it looks like its a common noise and not just mine!

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I've had two P38's with a ticking noise from the engine that I couldn't locate or identify.
The first was a 4.0 petrol. It let me know what the issue was when number 8 cylinder liner slipped, allowing the top piston ring to expand and ripping the piston, wrist pin and connecting rod into pieces.
The second P38 I'm still driving with a similar noise, It's the Callaway edition 163,000 miles and I stand on the pedal and blow down the Hi-Way at 97 MPH passing cars and trucks. Hasn't come apart yet?
These noises are near impossible for me to define even with an engine stethoscope, my feeling is the way sound is transmitted in a cast aluminum vs. a cast iron block. I've also had a 3.8 and a 4.6 Bosch (THOR) motor with no noise at all save for a little ticking in the rockers.
No help here, just my experience.

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Mine had the exact same noise, turned out to be worn rocker arms the pads the pushrod bear on were worn to excess..

New set of rocker arms shafts and pedestals solved the problem..

Sounds well now.

https://youtu.be/tho4PujSym8