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M275 V12 Bi-Turbo Platform Technical discussion relating to models sharing the M275 V12 Bi-Turbo (V12 TT). Including SL600, SL65 AMG, CL600, CL65 AMG, S600, S65 AMG.
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Mysterious noises M275 AMG SL65

 
Old 06-24-2018, 02:39 AM
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Mysterious noises M275 AMG SL65

Recently purchased this car knowing it had this rattling sound. Only noticeably audible from inside the cabin when warmed up and idling at low rpm. Noise goes away if I hold the throttle and raise rpm even slightly; noise goes away once I'm driving forward/backward (basically above idling RPM). Nothing changes whether I'm in neutral or reverse or drive; nothing changes whether I control the fan blower direction, temperature, or AC. I've noticed at night time (colder temperature), the noise appears a lot later (after a longer warm drive), and also sounds quieter compared to a sunny warm afternoon. If I shut off the car for 10min or so, I can startup with a chance the noise not being present, but would shortly appear again after it warms back up.

2 videos, inside and outside. Inside is very obvious. Outside not so much, even if under the car or inside engine bay.

Inside:
https://drive.google.com/file/d/1PxY...ew?usp=sharing
Outside:
https://drive.google.com/file/d/1AVb...ew?usp=sharing

I am clueless, anyone have any ideas?

Last edited by decadecivic; 08-21-2018 at 03:46 AM.
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Old 06-24-2018, 04:19 AM
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Welcome to the forums.

Good videos.

I would have a look at the clamping bands that hold the exhaust to the turbos.

After that check the exhaust mounting brackets.

After that the heat shield mountings - there are lots of them.

Are there any faults reported or other symptoms observed? Do you have access to SDS or an OBD2 reader?

Nick
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Old 06-24-2018, 12:14 PM
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Okay, I'll check all those 3 things very soon. Thanks for the direction. The only fault I have right now is relating to my Secondary Air Injection. I doubt that is related to this noise though. I have an Autel MOT Pro to pull codes and read live data if needed.

Originally Posted by Welwynnick View Post
Welcome to the forums.

Good videos.

I would have a look at the clamping bands that hold the exhaust to the turbos.

After that check the exhaust mounting brackets.

After that the heat shield mountings - there are lots of them.

Are there any faults reported or other symptoms observed? Do you have access to SDS or an OBD2 reader?

Nick
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Old 07-15-2018, 03:25 PM
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I got the car on a hoist and started inspecting the sound. I used a long screwdriver against my ear as a stethoscope. I've noticed that if I listened against the underside chassis driver side, the knocking sound would be more obvious than on the passenger side.

When I listened on this particular heat shield, I can isolate the noise. Moving or flexing the heat shield did not make the sound go away or any quieter.



When I listened on the heat shield that surrounds the steering shaft, it is the loudest and most obvious. I noticed that it was much more loose compared to the other heat shields, but moving it around didn't make the sound go away either.




Everything else I listened to, such as the cat converter, turbo, manifold, transmission, motor mounts, does not create or transfer that knocking sound. I am really confused as to why this noise would occur only when the car hot, and only at idling rpm. It seems like the noise is coming from the driver side firewall. I'm trying to look at component diagrams of the car and figure out if there are any motors, solenoids, etc, that exist at the driver side firewall, that maybe, once hot, would produce that sound. The most obvious source of the sound was when I listened to that heat shield surrounding the steering shaft.
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Old 07-20-2018, 12:27 PM
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bump. Anyone have any inputs?
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Old 07-21-2018, 12:55 AM
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Did you listen to ABC pump, a/c compressor or alternator? Try removing the engine belt and see if noise is still there
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Old 07-22-2018, 01:12 AM
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Change the pulsation dampener
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Old 07-22-2018, 01:13 AM
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Have you done motor mounts?
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Old 07-24-2018, 09:22 PM
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Yup, I probed those and the clicking wasn't from there. Like I mentioned, it was most prominent and obvious when I probed the chassis, front driver area. I could try and remove the accessory belt and run it, but will it be an issue on these Mercedes if I start & run the car without the alternator running?

Originally Posted by AmgSeahawker View Post
Did you listen to ABC pump, a/c compressor or alternator? Try removing the engine belt and see if noise is still there
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Old 07-24-2018, 09:31 PM
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I've recently purchased the car, not sure if they've been recently replaced prior. I did probe both engine mounts and they don't create or transmit the sound.

Originally Posted by g60wall View Post
Have you done motor mounts?
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Old 08-22-2018, 04:02 PM
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Does the noise change with accessory loads or if the AC is loaded/unloaded? This noise sounds like a damper in the AC pulley or the ABC pump itself.
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Old 09-07-2018, 01:16 AM
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No it doesn't. The only thing that affects whether the noise appears or not is if the rpm is low enough, idling, and if the car is warmed up. Also like I mentioned, I did probe the area near the driver side firewall, and the steering column heat shroud is the point where the knocking sound is the most clearest through the stethoscope.

Originally Posted by alexanderfoti View Post
Does the noise change with accessory loads or if the AC is loaded/unloaded? This noise sounds like a damper in the AC pulley or the ABC pump itself.
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Old 09-08-2018, 10:45 PM
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since you own the car now maybe contact the PO and ask him to come clean on anything he may know concerning the noise. I would get a cheep HF stethoscope and isolate the noise. You will be able to narrow down the area. Without the scope there's just too much coming at you.
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Old 02-01-2019, 01:54 AM
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To this day, still have not figured it out. The source of the sound is somewhere in the firewall area, underneath the windshield wiper unit. At this point, I'm guessing it is something loose that only vibrates when the car is fully warmed up and is allowed to warm idle at 500-600rpm. The noise gets annoying. I'm looking at potentially raising the warm idle rpm to maybe 600-800rpm just to make the noise go away. I know this would work because as I've mentioned before, I hold throttle a tiny amount so it cold idles at ~800rpm, rattle goes away. As well, when the car is still cold and the idle rpm is above 750rpm dash line, noise is not present.

Does anyone know if a Mercedes das/star xentry (im not familiar with these OEM softwares/tools) has the ability to adjust the warm idle rpm and raise it?
If someone can confirm it's not possible to do that, then the only other method I can think of to adjust the rpm is to 'trick' the ECU by modding the coolant temperature sensor. I could raise the warm idle rpm is by adding a resistor rated somewhere between 30Ohm-150Ohm in the wiring connector to the coolant temperature sensor. I have previously worked on other cars and used this method to 'trick' the coolant temp in order to adjust the warm idle rpm this way. I'm not sure how these Mercedes' ECU works entirely, but I know most cars have a proportional relationship between coolant temps and idle rpm. If these Mercedes works in the same principle, then I should be able to trick the ECU into thinking the coolant temps are at 80C and keep the idle rpm in the 700rpm range.
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Old 02-07-2019, 05:20 PM
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Originally Posted by decadecivic View Post
I could try and remove the accessory belt and run it, but will it be an issue on these Mercedes if I start & run the car without the alternator running?
No, warm it up until the noise appears, and then remove the belt.The car can work for some time with spark power just powered from the battery. But, I would not let it run for too long, because of the water pump(s?).

br,
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Old 02-10-2019, 02:39 PM
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Originally Posted by syljua View Post
No, warm it up until the noise appears, and then remove the belt.The car can work for some time with spark power just powered from the battery. But, I would not let it run for too long, because of the water pump(s?).

br,
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Yes, do this. Raising the RPM to remove the sound is not ideal, that noise shouldnt be ignored.

You can raise the idle by 50rpm in STAR.
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