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*Premium Member
2005 SLK55 AMG /2005 SLK350
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6,192 Posts
Discussion Starter · #1 ·
I've got a sound like two or three steel ball bearings inside a five pound coffee can that's being shaken. It comes and goes though - not constant. It's worse at cold start, and doesn't seem to start until I drive off. At first I thought it was a loose exhaust pipe rattling up against something, but an inspection of the exhaust turned up nothing unusual.
 

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Founding Member 2006
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108,971 Posts
beginning of this video

 

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*Premium Member
2005 SLK55 AMG /2005 SLK350
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6,192 Posts
Discussion Starter · #5 ·
That's what I'd call a constant grind - like an alternator or tensioner pulley. This sounds like industrial popcorn popping, and it comes and goes.

I'll get it on a rack for a better look this weekend.
 

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Founding Member 2006
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108,971 Posts
It is your catalytic converter!! :D :D
See my video in Chris's post above.
 

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*Premium Member
2005 SLK55 AMG /2005 SLK350
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6,192 Posts
Discussion Starter · #8 ·
TY I will check the cat first. I'll make a video of the noise once I get it in the air.

What's surprising is it comes and goes. Do you think this is a case where the internals of the cat have come apart?
 

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Founding Member 2006
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108,971 Posts
yes!...........
 

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Founding Member 2006
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108,971 Posts
I still say supercharger. put a stethoscope to it :D
 

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Founding Member 2006
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108,971 Posts
I've always said sc. I was only razzing Chris before when he said cats but after listening, it sounds like the wheeler dealer video when he put the steth on it :D
if does not make noise when stationary, then I move to a loose hinge or exhaust linkage
 

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*Premium Member
2005 SLK55 AMG /2005 SLK350
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6,192 Posts
Discussion Starter · #15 ·
Found a broken exhaust bracket between the transmission and the downpipe... I missed that on my first inspection (bad light, bad weather, bad mechanic).

MB says "no longer available", heading to the muffler shop tomorrow AM to let them have a crack at welding it (bad pun I know).

Jury is still out, but I'm 99% sure this is the cause of the noise.
 

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Founding Member 2006
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Yay!!!!! do i get partial credit?

if does not make noise when stationary, then I move to a loose hinge or exhaust linkage
 

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*Premium Member
2005 SLK55 AMG /2005 SLK350
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6,192 Posts
Discussion Starter · #19 ·
Well this is truly maddening... totally silent when parked on level ground, regardless of RPM.

And the sound, although greatly reduced, is the exact same sound as before. Makes me think the source of the sound is the same, but just with less input.

I revisited all the exhaust hangars and brackets this morning, all are intact. Upstream there are two steel brackets bolted between the transmission and downpipe (ahead of the dual cats); downstream there are three rubber donuts (one ahead of and two behind the final resonator). The two steel brackets are perfectly rigid - the geometry between the exhaust pipe, the engine, and the transmission has no play. And there is plenty of clearance downstream - the rubber donuts are solid.

I'm going to take a $150 gamble and order new mounts. In the meantime, I'll remove the airbox, inspect the heat shield above the header, and replace the supercharger oil.
 

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*Registered
2003 SLK230
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679 Posts
It's likely still an exhaust hardware issue. The reason it's quiet in park is that there isn't much load on the engine. When accelerating in gear, the engine will move against the mounts and expose any poorly installed or loose exhaust components. The cheapest fix is to crank up the radio.
 
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