Hello guys, I recently purchased a 2007 c280 with 35k miles and I've been reading on these forums since and cannot stop! We used to drive a ford before until it finally gave out, then we decided to get something else. Ive never been so interested in cars before but after I started driving the benz, it all changed. I have so many questions about upgrades, mods, detailing, etc. but the most pressing is this one.

When I am driving the car, I start hearing some tapping noise from the engine. It doesn't happen right away but it always occurs after about 5 minutes of driving. I will include a link below to a recording of it because I don't know how to accurately describe it.

http://dl.dropbox.com/u/245810/c280noise.mp3

I recorded that after driving around for an hour or so, you can clearly hear it towards the end of the clip. If anyone has heard or experienced this before, please let me know and what you did to resolve it. I personally dont think that the engine is suppose to sound like that but let me know what you guys think. BTW, the AC was off, nothing else turned on. Again, I really am a beginner when it comes to knowing cars inside and out, but I am well on my way to learning.

Also, there are other things that I am noticing. When I have my foot on the pedal and I release it, the car should slowly decelerate. For some reason, when I am driving the c280, it feels like I have my foot lightly on the brake. It tends to slow down faster, ironically. I notice the difference so much when I drive the benz as compared to when I drive my brothers car. Again, I dont know if this is normal, or a possible issue. Could it be related to the engine noise?

Any input is appreciated.
Thanks guys, this forum has been great.

 

anyone know what the cause might be?

 

Hi there i can't hear the sound clip. Is it when you rev the car between 1200 and 1500rpm.

 

the link should work, just did for me. Try right clicking and save as. Not sure if its between that rpm range, but it is most noticeable when the car is idle.

 

i listened to it but really couldn't here anything. (Just came from a concert when i listened to it so maybe that was why lol)

 

hah yea probably, the recording is faint because I did with iphone. If you listen to with headphones or put volume up you can hear it towards the end.

 

Oh I hear it there near the end of the recording. Something is definitely up with that, not a normal noise at all.

If it is a 2007, it should still be under warranty. Don't worry about it - let the dealer figure it out!

 

I get that alot, I made a thread about it somewhere, one of the senior members stated it was just some noisy pistons. When you give it some gas it goes away, right?

 

Laneshift - you have the M112 and his car is the M272. It's a completely different engine. I don't think what his is doing is even close to being a normal characteristic.

 

OK - let's handle the easy question first. Benz 722.9 7G transmissions run with the torque convertor locked up 99.9% of the time. When you lift off the throttle the car is running against full compression just like a manual does so it will stand on it's nose as if you applied brakes. This is done for efficiency - no more yankee slush box!!!!

When I listen to your clip it is extremely indestinct this end at full volume. It sounds as though the "knocking" sound is not related to engine RPM. Is this correct? If so it effects the diagnosis drastically - ie. it can't be a hydraulic lifter stuck, piston slap or a small end bearing if not RPM dependant. Please confirm if the noise is RPM related.

 

The only difference between a 112 & 272 are the cylinder heads - Twin cams per head - Otherwise the engine is identical.

 

I took it to the dealership in Astoria, Queens yesterday and the guy told me it was the MOT valve. He said it is entirely normal. Can you guys confirm this?

The noise seems to be somehow related to RPM. When the car is idle, the tapping is at a constant tempo. Once I start revving up, the tapping start to become faster until I cannot hear it anymore due to the engine being loud.

 

Pretty much.

 

The purge valve on some cars can be noisy. Replace or mount it on rubber to shut it up. A kit is available.