Noise under load, rattling cat?

[M104]

Hello everyone,

Here's the irritating noise i have to deal with: It is only present under load from 2000 to 2500 rpm and i can't replicate it by just revving the engine in park and it is not present at idle. It really sounds like a can full of marbles and i can feel a bit of exhaust vibration through the floor.

I haven't found anything loose anywhere, heatshield are all properly attached and there's no contact between the exhaust and the undercarriage or anything else. I've just made an audio recording while driving with the windows down and close to a wall as well as a short clip of the tiny metallic zing sound it makes when hitting the cats with a rubber mallet.

Sound almost like a piece of wire or a spring is caught in there. I have zero idea if both noises are related or not. I'd like to rule out every other possibility before doing anything related to the cats.

The car is a 96 Mercedes W210 E280 inline 6, 139k km.

 

[Jetronic]

there could be something loose in there, but my experience with the actual cat being loose in the can is it kills power a LOT. backpressure goes up significantly when the cat is misaligned, killing performance.

Have you checked the flexi joint is still intact?

 

[M104]

Have you checked the flexi joint is still intact?

It doesn't have a flex joint. It has two donut gaskets, one after each cat before the first muffler but everything is tight.

 

[Kira]

Could the muffler's internals be causing this noise? Do you know it's the cat?

 

[M104]

Could the muffler's internals be causing this noise? Do you know it's the cat?

I don't know for sure. Both mufflers where recently replaced by the previous owner. The noise comes from the area of the catalytic converters when i try hitting everything with a rubber mallet. I've been told the noise while driving sounds like a cat too.

 

[2strokeNorthstar]

I bet the cat is breaking apart. My F150 kept getting worse until it started to rattle even at idle. Became embarassing so I replaced it with a new bolt in section including 2 cats. The catacomb (name?) Was complety separated and just floating around in the can when I took it apart. I gained a little noticeable performance when under heavy load but not dramatic. The OEM are worth $$$ even when damaged.

 

[M104]

I've made an observation: there is water dripping from these flanges on a cold start which indicates a leak. Is it possible for a small leak to cause the noise heard in the recording? The leak isn't big enough to blow enough air to be felt with the hand.

 

[M104]

I am often driving with the windows down now that weather's getting nicer and this sound is annoying as hell. I've read that it is common for this generation of Mercedes to have rattling lower cats if there's a thermal shock such as driving over wet grass of spraying cold water while the cats are hot.

I'm almost about to drill two holes at the bottom of each cat and try to crimp the honeycomb a bit with screws. Has anyone ever done that? Before you ask, there's no replacement cat available for my car, new or used.

 

[D60]

I'm no help but let us know what you find

 

[M104]

Sure will!

 

[MaximumMini]

If the dripping doesn't smell of anti-freeze, it could be normal condensate from the catalyst doing it's job.
But unless you have loose connectors somewhere, my money would be on bits of the catalyst breaking off inside and rattling around.

 

[Thebigm]

there could be something loose in there, but my experience with the actual cat being loose in the can is it kills power a LOT. backpressure goes up significantly when the cat is misaligned, killing performance.

Have you checked the flexi joint is still intact?

Pre ignition?

 

[M104]

Just came across a video of a W220 S430 making the same noise and it turned out that the previous owner gutted the cats! Really curious to see what's in there.

 

[ARCOgraphite]

On My Nissan it was broken loose spot welds on the front heat shields. Made quite a racket.

On my Wife's Hond civic it was a crumbling cat.
On my Wife's Subary Loyale it was some nasty co-woker putting pebbles into her exhaust pipe!

 

[2strokeNorthstar]

On My Nissan it was broken loose spot welds on the front heat shields. Made quite a racket.

On my Wife's Hond civic it was a crumbling cat.
On my Wife's Subary Loyale it was some nasty co-woker putting pebbles into her exhaust pipe!

I've only been lucky enough 1 time for it to be the heat shield.

 

[M104]

I've decided to drill a few holes in the cat making the tiny rattle when hitting with the fist to try crimping the honeycomb with screws as a temporary fix but to my surprise, it wasn't separated from the casing! Now i am wondering what's making this ringing sound when i hit the cat and is it really the cause of this obnoxious noise.

I do have an exhaust leak at the joint between the two mufflers but it's not too bad and i doubt it could be causing this racket...

 

[Zee09]

On My Nissan it was broken loose spot welds on the front heat shields. Made quite a racket.

On my Wife's Hond civic it was a crumbling cat.
On my Wife's Subary Loyale it was some nasty co-woker putting pebbles into her exhaust pipe!

Mitsubishi and Subaru are good for the heat shield fiasco up north with the salt etc