My 04 MCS has develloped a strange, very high pitched "whistling" noise that seems to come from the supercharger under some fairly specific conditions:

• The noise shows up between 2500 and 3200 RPM.
• It happens only when the engine is under acceleration and under load (pressing the accelerator and driving up a hill, for example).
• I can interrupt the noise briefly by pressing and releasing the accelerator slightly (modulating the gas pedal). If I take my foot off the accelerator suddenly, the noise goes away only to return when I accelerate again.
• There is no noise when the car is coasting or if I accelerate while driving down a hill.

The biggest issue is that when I drive the car on the highway at cruising speed (around 120 Km/h) in 6th gear, the engine is running at around 3000 rpm so the noise is fairly constant. I am currently forced to either accelerate to 130 - 140 Km/h or downshift in 5th to keep my revs up which eliminates the noise but also drives up my fuel consumption.

I had the car checked at my dealer and they claim this is "normal supercharger noise". This "normal" noise wasn't there since I picked up the car last September and only began about 3 weeks ago. Other than this the car runs great and I'm very happy with it.

Internet searches bring up some similar issues related to either a bad intake manifold gasket or a leak in a supercharger hose but I want to know if anyone else on this forum may have had a similar issue with their MCS, and if so, what was the cause.

Cheers,

M

 

This is a normal sound, although it can become louder when the windows are open. It can also be caused by the by pass valve opening prematurely.

 

If it was a normal noise, I would guess it would have made it from the day I got the car. It did not make this noise all winter, in fact it only started a few weeks ago. You can hear it quite well if the windows are closed, even more than if the windows are opened.

 

Sounds like throttle plate whistle to me. Do you have any mods?

 

No mods whatsoever. Car doesn't even have cruise control. Barebones MCS with the Sport Package (Sunroof and Xenons).

Throttle plate whistle sounds logical but why did it come up all of a sudden?

 

When did you get the car? It could be weather dependent (although that is not the case with mine). I am going to take back my original diagnoses only because of the fact that I dont have to be under load to get mine to do it. That said another NAM member, Blimey Cabrio, went through a big "adventure" with throttle whistle. He would be the one to ask.

 

Thanks for the feedback. Got the car last September but I only really started noticing the throttle noise a few weeks ago and it only happens within that narrow RPM range while accelerating and while the car is under load. Don't notice it in 1st but I hear it in any other gear. It is most noticeable in 6th while cruising down the highway.

I may take it back to my dealer later this week and I will try to locate Blimey Cabrio. Cheers!

 

Check the idler pulley. Mine was making noise but couldn't pinpoint what it was. Once the idler pulley finally seized, then I knew what it was. Replaced the idler pulley and the noise was gone.