Hey guys when pulling in my garage after driving home, mostly highway and some hilly backroads I get this high pitch squeal from the front of the engine. It goes away when the engine is revved. Can't seem to figure it out, have checked all vacuum connections and doesn't appear to be a pulley. Please help! Is it a vacuum leak or a pulley?? Thank!

First video is with the noise and the second is how the engine normally sounds.

Lol gator in the first video there is a very high pitched squeal that is not present in the second. It goes away when throttle is applied. I am starting to think it may not be the tensioner. Any other thoughts?

Belt is genuine MB and has approx 5500 miles on it. Sprayed water on the pulley and obviously running it with the belt off would be a sure way to tell. Fan clutch removal is a PiTA anyone know where to get a removal tool? Anyone ever heard the noise in the video before?

Update. Car does not seem to do it at idle any longer. Only when put into drive. Hey gator, doesnt seem to be coming from the transmition and more towards front of engine. Now I'm stumped!

I suppose it could be. But it only happens randomly and will not happen in neutral but will in drive would more tension be on the belt? I've used some belt stuff and did the water test. Can't hear it in the cabin but can if the window is down. Sometimes happens after going around a turn. Could be the idler I suppose but the inconsistency is throwing me off. Wish I had a fan removal tool it's a pita to do it from underneath and then also it doesn't always happen unless the cars driven so guess best thing I can do is try!

Update sound still will only happen in drive or reverse. If I leave the car in neutral and rev the gas it will come but then go away.

Ruled out idler pulley by replcing that today. Could it be the injectors?

Heres another video you can hear the squeal and it goes away when put into neutral or park

Lmao bro you're on a half dead forum and putting up worse responses then I saw on cobalts.net in 2010. You might just be too old to pick up on the frequency of the sound tbh, then again I was a sonar technician in the navy.... but... I work at a dealership and have a tech who was at Mercedes for 12 years. I've been losing coolant pretty much since the issue started. Thinking it's gonna end up being a vacuum leak in the coolant system after replacing every single component except the auxiliary pump. Replaced that, starting getting a vacuum leak noise not egr related so must be that. Will let you know. Thanks!