Buck74

I have a 2010 GLK 350 with 121k on it. No one seems to know where this dam ticking /knocking noise is coming from

Mmr1

You need direct the sound to your ear and then locate the sound, a simple broom handle or pole touching your ear and the motor will help you locate the sound. You can buy a Auto stethoscope for this but a pole will do the same thing.

CarbonKevinYWG

Never heard of a solid rod, I prefer using a hollow copper water pipe, sound travels inside it really nicely. But a $10 automotive stethoscope really can't be beat.

PACIFICMAN

A long ratchet extension works beautifully.

Mcosman1025

did you ever find out what it was. My 2010 GLK 350 4matic with 133000 also makes a loud ticking noise when I start it in the morning. The colder it is outside the louder it gets.

Odd Piggy

Sounds like a bit of excessive play somewhere in the valve train. At 133k a bit of wear can lead to a temperature sensitive ticking that goes away as the parts heat up. As long as it goes away, or gets much better, as the engine warms up, it’s not a problem.

Mcosman1025

thank you so much for responding back

habbyguy

I'd suggest spending a few (literally) dollars and buy a mechanic's stethoscope. Harbor Freight has a workable one for around $5. With it, you can find the actual source of a mechanical noise (or at least eliminate the things that aren't a problem). There are a whole lotta moving parts in play and many of them could potentially make the noises you describe.

Silver Shadow

My 2010 GLK350 is the opposite. It's quiet when cold and ticks once it's heated up. In over 3 years of ownership the sound hasn't changed. I just call it the Mercedes sound. Our BMW is silent.

MB_Tor

Had the same issue. In Canada, this was the part replaced and Cost.

Secondary Air Pump
Remove and Replace components as required to access and install materials, and/or perform needed service. Retest and verify repair as required. Perform final road test where applicable.
Air Pump 1 Unit $558.20 / Unit $558.20 EH
Relay 1 Unit $25.68 / Unit $25.68 EH

habbyguy

Here's the mechanic's stethoscope I have (I have two for some reason). Not pro quality, but a lot better than using a rod or broom handle. ;-)

https://www.harborfreight.com/mechan...ope-63691.html