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Discussion Starter #1
So, I started noticing that exhaust has a rattle when I push the car hard. It comes around 3K and goes away around 3.5K RPM. Very annoying. It also makes quite a racket at cold start but after few mins of warm up the rattle goes away. Had the dealer take a look at it. He took a rubber mallet and tapped the entire exhaust and fund slight rattle in the rear section (after catalectic converter). He put in a part request. First I was under the impression that they will replace the exhaust but later I found that they ordered heatshield and bracket parts that holds the exhaust. I have taken an appointment for Friday to get the parts replaced. Will keep you guys updated. The sound does feel like a loose heat shield. But when the car was up on the jack I could not see any heatshield. Not sure. Any pointers?
 

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Premium Member 2013 SLK350
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A few threads exist on the R172 SLK sub forum describing all sorts of rattles and noise from underneath our cars. These have been associated with the exhaust manifold (prevalent in the 350/300) as well as catalytic converters.... Mine has had 2 replacements of the catalytic converters.... (left and right)... in fact, the last one was just replaced a couple weeks ago. MB is aware of these issues and should do whatever is necessary to fix yours.
 

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Discussion Starter #3
Thanks for the quick reaply! I did search this forum and did not find any one complain about rattle with SLC 43. Not sure how many exhaust parts are in common between SLC43 and SLK 350. Lets hope dealer is sincere. Will know soon.
 

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The dealer changed the entire exhaust section (after cat converter). It is all on piece - welded together. The swap took less then 20 mins. Very impressive service. I tipped the mechanic handsomely for taking such good care of me. The car sounds proper now. I hope it stays this way.
 

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The dealer changed the entire exhaust section (after cat converter). It is all on piece - welded together. The swap took less then 20 mins. Very impressive service. I tipped the mechanic handsomely for taking such good care of me. The car sounds proper now. I hope it stays this way.
Good to know, I get the faintest rattle right at startup but goes away within 10-20s not to come back until another cold start.
 

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Discussion Starter #6
My car still exhibits slight rattle on cold start - and like your car it last only for 10 to 20 sec. It is coming from under the car. Feel free to record the sound and post it as youtube video. I will let you know if mine sounds similar.
 

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Discussion Starter #7
I noticed you have the red art edition. Mine is Red Art as well. Perhaps it has something to do with the color? :)
 

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Discussion Starter #8
I got the faint start up rattle checked again by the dealer. I left the car with them for three days and the mechanic had the chance to cold start the car couple of times at least. He detected it to be waste gate related. I told him not to do anything as it last only 8 Sec on cold start and one has to listen really hard to notice it.


I tip my mechanic handsomely and I go to the same guy all the time. Situations like this they go the extra mile.


The dealer gave me a loaner car while my car was being checked out. I reached late and all the regular loaner were out so they pulled a new car from the lot. SLC300 with 10 miles. This is the first time I drove the 2L turbo engine and I was genuinely impressed with this little motor. If you put your foot down then you are greeted with a terrible turbo lag but in a normal day to day driving situation this motor feels fine. It does make some agricultural noise but the cabin so well insulated that one does not hear anything from inside. The fit and finish of the car was perfect. I could hear slight waste gate rattle on cold start from this car also. So I am beginning to see a pattern with these new turbo motors.
 

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Registered 2016 SLC43
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I have an older SLC 43 (Sept 2016) but honestly don't have any rattle on cold start or when driving. I also test drove 1 other 2016 and a 2017 and didn't notice anything. Is this peculiar to the 2018 model or have I just been lucky?
 

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I have an older SLC 43 (Sept 2016) but honestly don't have any rattle on cold start or when driving. I also test drove 1 other 2016 and a 2017 and didn't notice anything. Is this peculiar to the 2018 model or have I just been lucky?

Lucky you. When the engine is cold the catalytic converter is also cold. During cold start the waste gate opens and removes all the hot air from the turbo (turbo spins less) along with air from the secondary air pump and heats up the cat real fast. Mixture is also made rich during this time and the added air /oxygen from secondary air pump creates an additional source of heat in cat. Hot cat is more efficient to reduce emission so in theory sooner you can get your cat heated less damage to the environment. About 8 to 20 secs.


In our case - the problem lies with the arm that pushes the waste gate valve. The spring which holds the tensions is now less effective as the arm is fully extended and hence the rattle. Waste Gate Arm Adjustment is an art more than science. It is apparently threaded ( I don't know this for sure). If you the thread is extended too much it rattles. If it is too tight, you will feel little turbo lag. BMW turbo's are plagued with this problem.


If it bothers me too much, I will fix it myself. I will buy the counterfeit shop manual from ebay and give it a shot. There are so few of us with slc43, I don't have any reference material for the adjustment.
 
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