I'm getting this high-pitched whistling sound that only happens at wide open throttle between 2nd - 3rd gear. 2018 C63S. Doesn't seem like there's any loss in power, but still seems odd.

Anyone else experience this?

https://mbworld.org/forums/c63-c63s-...ml#post8099413


https://mbworld.org/forums/c63-c63s-...ml#post8102493

Have a read of the above, possibly the same noise, probably “normal”. My car is a 2018 PFL

Best guess is a vacuum leak somewhere: A clamp not tightened down, bypass valve's leaking, etc.

The whistling symptoms could be caused by the air at a certain load/rpm/boost combo that happens to create a whistling effect - but would still bet it is leaking at other times as well. ( If it is in fact a vacuum leak)

It is not surprising that you would not notice a loss of power if the leak is small.

I would start with the easy free stuff like checking/tightening all vacuum hoses for wear holes, clamps, bolts and operation of bypass valves, etc.

If you can't Identify it, just take it to a qualified shop and they will probably do a vacuum or smoke test.

Edit: After reading the 2 threads above, I have actually had that symptom intermittently as well over the last 2 years. Same thing happens at WOT, high rpm, not every time. I can hear it, then do the same pool immediately afterwards, its gone.

I have tossed around 2 theories:
1. It is the blowoff valve leaking at max load/stress, especially if running a tune with higher boost levels.
2. It is the ECM/traction control interfering is some specific circmstances through electronic manipulation of the bypass valves, in order to help maintain traction or something. Idon't think it's ever happened with the traction control fully off, and does seem to happen more when immediately preceded by tire spin, especially when turning. Unfortunately due to the intermittent nature of the whine and the fact I rarely drive around with the traction control fully off, that may just be coincidence or obsevation bias.

I still suggest the same course of actions I mentioned above though, even if just to eliminate the possibility of a vacuum leak.

Anyone else notice this high pitched heeee noise on WOT only happens after a cold start but eventually goes away after the car is really warmed up and driven it hard?

I heard it today and it disappeared after I gave it a good flogging in Sport+ mode 🤔🤔🤔

I'm really leaning towards pulleys and belts. Going to try again tomorrow with the aircon off..........

Hey everyone I recently hit 29k miles on my 2018 C63s and started noticing a weird sound on WOT up shift when I click the paddle.
Its a very faint squeak or like "heeee" sound from what sounds like the area right behind the upper dash area or behind the gauge cluster which would be the upper portion of the air boxes in the engine bay. Its only in 3rd gear when I use the paddle shift or full Manual mode Sport plus or Race mode. Only mods are AFE Pro dry drop in filters and I feel like it just started recently doing this sound. Ive had the filters in for about 1000 miles but other than the weird sound only WOT near redline shifts in 3rd gear I cant hear anything else. Any help on what to inspect or information would be greatly appreciated. I might swap back in the OEM filters to see if it still makes the sound for my first test to narrow anything down. Im going to try to do some WOT pulls and let the car shift on its own and listen to see if it makes the sound in auto mode as Ive only heard it while in Manual mode or auto but manually shifing.

Im getting a high pitched like heeee or weee sound on WOT 3rd gear upshift near redline in sport plus and race mode. Cant find a solution either. 2018 c63s 29k miles and stock.

Quick clip to show the sound I had described in this thread.

When I hear the word "whistling" sound I was like hmmm that must be the turbos. When I saw your video, I am not sure about it in your car.

Unlikely the cause but check your air intakes as well, if you are not getting full boost at WOT, then it might be a loose air intake, the plastics are super flimsy and so easy to to be unclipped or not clipped on properly when doing an oil change for example. The sound of which that forum member described as a "dentist drill", not the same model, c43 vs c63s but very similar air intake design in the c63s with those plastic clips. https://mbworld.org/forums/c450-c43-...ml#post7825169

In case it helps someone else, this sound ended up disappearing after I got my transmission serviced. Still not sure why it was happening, but it seems that simply changing the transmission fluid & filter solved the problem.

Hmmm might be incorrect level then but glad it got solved thanks for the update.

Can 100% confirm this is the stock turbochargers now because after I changed the turbos in mine I never heard this whistle again. But don't worry too much my Coupe had this whistle noise from almost new and I drove it hard like that for 30,000 miles and they never missed a beat. It's just one of those irks.

Thanks for confirming