Loud intermittent rattle on startup.

[mbrightside]

Hi, got an awful noise developed which seems to be worse just after starting. It changes intensity with idling speed. I have put a video on YouTube https://youtu.be/4E_SwvBxiUI

You can hear the noise reduce about half way through after the engine has revved.

It appears to be coming from the rear left of car. Pretty sure that it goes away after being driven for a while, definitely seems to be less pronounced after warming up.

Any ideas as to what it can be?
Thanks in advance...

[fatmike]

Probably just the heatshield. Re-attach it, or just rattle on.

/

[Mig]

Either a loose heat shield or might be the inside of the catalytic converter has become detached and is rattling around.

With the engine off, tap the catalytic converter with a rubber mallet and see if you can make the same noise.

Hopefully it's just the heat shield.

[BIGJake111]

I have a heat sheild that does that. I put a clamp on it. It now oddly only does it at exactly 1k rpm until things warm up.

[Timco]

Use your fist to pound around in the trunk with car off. If heat shield you'll hear it.

Mine made an awful rattle. It was the water pump scraping the engine block.

Chain tensioners have been said to cause start up rattle too.

[Smallblock454]

As said catalysator heat shield. These are holden by DZUS fasteners. In general they rust away and you have to replace them. Expensive.

Regards, Markus

[geraintthomas]

Mine was the O2 sensor that went into the exhaust at the back, it was loose. I just tightened it and all was fine. But I also found that the heat shields for the cat convertors are missing, so the previous owner had removed them for rattling also.

[nieuwhzn]

My left cat heat shield rattles. Once in a while I jack up the car and judicially hit the shield with a hammer. That fixes it for a while. Still trying to find time to replace the secondary cats with test pipes which will also solve the heat shield rattle.

[RandallNeighbour]

I had heat shield rattles/buzzing a while back and when I discovered what it was (thinking it was MUCH worse) I took a hammer to it and beat the crap out of it and wow, that was a lot more satisfying than I imagined.

[shacky]

I just got this as well. I had previously heard it on downshifting after it got hot. Now it's at idle at start up. Sounds like crap and Porsches shouldn't sound like crap...

[mbrightside]

Think it's the cat, tap it and it rattles, plus a think the heat shields have been removed by previous owner... What the hell do they look like anyway !! Thanks for replies all!