Erval9

Hello,

I recently bought a 2014 base GLK350 V6 3.5L. It has 70,000 miles.
The car makes a loud "revved up sound" after driving for 30 minutes BUT ONLY when I put it on P-park. It doesn't go loud when it is on R, N or D, only when I put it on P and leave it on idling.

I am not experienced with this engine/type of car and I want to know if it's normal for this car to do this sound.
My theory is maybe a clogged vacuum line but I am not experienced with engine sounds, especially for this model.
It only happens when I put it on P after having been driving for a while and want to turn it off, it sounds normal when I'm driving. The engine sounds revved up but the RPMs remain low (below 1000).
It sounds like a laptop that is getting too hot but in "car version". It goes back to normal engine noise when I put it on D again or after letting it sit for a few minutes (like 5+minutes).

The previous owner said, he did the regular maintenance oil changes, brakes, battery but that's about it.
I'm thinking doing a tune-up soon. I'm gonna replace the oil and oil filter, spark plugs, transmission fluid change, air filter, cabin air filter, belt looks good.
What recommendations would you suggest?
Do any of you have any experience with this? The loud sound only goes up when I switch from D-Drive to P-park after driving for a while.

Thanks.

Odd Piggy

My first thought is the radiator cooling fan. But the “only in PARK” part is sort of confusing.

Erval9

I don't think it's the fan. Fans don't make noise louder than normal since it's air that pretty much stays at the same velocity.
The sound is definitely coming from the engine. It only increases in "loudness" once I put it on P-Park and after driving for a while.
It sounds like I'm putting the foot on the accelerator at 2000RPM except I'm not and the RPM are normal at below 1000.
It goes away after like 5 minutes or so or when I put it back on D or R.
It's got to be a defective valve or vacuum line. I'm trying to research and see if people have had this issue too.

Odd Piggy

SAFETY WARNING: You must stand near a running car to do this check. Set the parking brake! Do not stand in front of the car! Stand off to the side nearest the oil filler cap. If the car were to inadvertently shift into gear while standing in front of the car, you could be killed.

There is a crankcase vent valve. When it fails, a screeching noise like a slipping fan belt is heard. It does not happen at startup and only begins after the car is warming up 4-5 minutes later. You can check to see if it’s that valve by removing the oil filler cap with the car running in park with the parking brake set. The noise should stop suddenly when you do this and resume when you put it back on.

SAFETY NOTE: Do not place your hand over the oil filler hole with the engine running! Only use the oil filler cap to close the hole! There is great vacuum there and you could be seriously injured!

Erval9

Yeah I've read about that. My car doesn't make that "screeching noise". It just revs up when say, I'm back home from work about to turn off the car. When I put it on P, the loud engine starts. It could be what you're talking about and my car is just reacting differently instead of screeching.

Mmr1

Post a video , 1000 rpm is high at idle . Maybe the fan but mine is fairly quiet when running , get the codes read . Most big auto parts stores should do it free while you wait in a few minutes.

Mmr1

Are the fans on when this happens ? If you turn on the AC you can hear how the fans sound, if the fans are on high when you hear this noise something is saying you are overheating