MB Ticking / Tapping noise only when warm

[FreeWoRLD]

Hey guys,

I have a 2018 MB GLC300 and have a strange tapping noise. I was wondering if anyone has any idea what might be causing it.

How it sounds;
Camera can't pick it, no matter how I tried it, but it is very clear in person. It doesn't sound like a mechanical noise but I can't be sure. Tapping would be a better word to describe it

How to replicate it;

• Never happens on cold engine (after vehicle sits overnight in cooler temperature under 40f.
• As the engine warms up the noise starts but faint
• The strongest and loudest noise happens when vehicle parked after the first drive session in the day. So for me, it happens every day when I am heading back home after work
• The warmer the weather, the sooner it starts even if I start the first time in the day
• Never happens revving up when vehicle is stationary - no matter how high you revv it up, or either at idle. Engine is very quiet and smooth honestly, when idle or revving up.
• Only happens when accelerating. If I put it on neutral when driving, the noise immediately goes away. Also it goes away if I release accelerator. So, basically it only happens when on load and accelerating.
• It also goes away after 50mph or so and 6th gear or up (on 9 gear auto transmission)

Oil changes does have no affect and transmission fluid was changed by the dealer 15k miles ago. I have never used regular gas ever and mostly had shell premium, occasionally QT.

So, what could be the issue? Thanks

 

[dadto2]

Did a neighborhood kid put some zip ties on your driveshaft??? Maybe you're that guy who hands out toothbrushes on halloween? lol

 

[vavavroom]

I'm not convinced it's the engine.

 

[FreeWoRLD]

I'm not convinced it's the engine.

I don’t think it is engine, either. Buttery smooth at any RPM, as long as transmission is not engaged. So, what is it - I don’t know. My other suspicion is anything with exhaust, but in that case, why the noise is there only when on drive and accelerating - but not in neutral at any rpm

 

[We're Metals]

Probably high pressure fuel pump

 

[twX]

Engine noises that only happen under load are often rod knock or piston slap. Valvetrain or timing system noise should only be affected by rpm, not engine load.

If the noise goes away at higher speeds in higher gears (and you know it's not just the road and wind noise masking the sound), it's probably not engine related. The transmission is a suspect. Check its fluid level.

 

[JHZR2]

MB uses lots of rubber donuts and other blocky exhaust hangers. I suspect it is the exhaust. My 1991 has a metal to metal thst only happens in some cases at around 2k rpm. Don’t forget that the exhaust system can grow and shrink a bit as it heats and cools….

Check your hanger rubber pieces!

Coukd also be a leaky lifter but I’m not as convinced.

 

[MaximaGuy]

It's the HP fuel pump got mine replaced under warranty. It sounds like a diesel engine under idle. Its a real expensive job $2000 for a $50 part.

BTW the ticking noise is also at speed you just don't hear it with the road noise.

 

[dumkid]

Hmm typical Mercedes noise. Does it make a nack nack sound about 300 times a minute?

 

[FreeWoRLD]

Here’s an interesting finding.. When noise is there, if I get a car wash (with underbody), noise goes away completely right after the wash. Engine is not turned off during the washing.

 

[FreeWoRLD]

Do you guys think this could be something about exhaust?

 

[KrisZ]

Here’s an interesting finding.. When noise is there, if I get a car wash (with underbody), noise goes away completely right after the wash. Engine is not turned off during the washing.

If that’s the case, the issue may likely be with the accessory belt or one of the accessories.

 

[FreeWoRLD]

If that’s the case, the issue may likely be with the accessory belt or one of the accessories.

Thank for your comment. Do you mind letting me know what you think exactly is happening when car is being washed, for the noise to go away?

 

[KrisZ]

Thank for your comment. Do you mind letting me know what you think exactly is happening when car is being washed, for the noise to go away?

Soapy water provides temporary lubrication either for the belt itself, so it stops making noise or for the bearing in one of the pulleys. Could be an idler or tensioner pulley. That would be my starting point.

 

[FreeWoRLD]

Soapy water provides temporary lubrication either for the belt itself, so it stops making noise or for the bearing in one of the pulleys. Could be an idler or tensioner pulley. That would be my starting point.

Appreciated