Buzzing noise from engine compartment when car is parked

[cdonner]

I noticed that until several hours after driving my 2009 C-300 Sport (manual with Entertainment package) I can hear a brief buzzing noise, about once every 30 seconds or so, that seems to originate from the engine compartment. Have not been able to pinpoint the source of this noise.

Does anybody know what it is and where it is coming from?

[cb0473]

I hear the same buzzing noise you described on my 2008 C-350.

[Moto_Guzzi]

I have heard it once on a warm day last summer, opened bonnet, and found black electric waterpump near water bootle buzzing, could feel it.

I also hear another buzzing sound sometimes after starting the car and out of driveway for a few seconds then it goes away, not sure what this is.