Noise when locked and parked

[ivegotcclass]

I've noticed that my car makes a humming/buzzing noise when it is parked, static and locked. It does seem to be more when the car is locked, is there something that is running such as an immobiliser or cooling system?

It is a very strange sound and the car can still be making this a few hours after it has been driven.

55 plate C220 CDI Sport Coupe

 

[jberks]

I get some very odd noises out of my E270CDI when it's parked too. Buzzes, high pitched whines etc. I haven't listened hours after parking but certainly 30 mins or so it can often be heard talking to itself. Never figured out what it is but everything seems to work happily enough the following morning.

 

[ivegotcclass]

Sounds very similar, anyone else have any similar experience?

Can it be narrowed down to diesels, immobilser, cooling system, etc?

 

[Rory]

Wild guess - maybe it's the high pressure fuel system gradually de-pressurising?

I have a 54 reg C270CDi and I live in a very quiet place, and I've never noticed anything other than COMAND fan running for a few mins after the car shuts down, but I can't hear that from outside the car.

 

[jberks]

Possibly. The Jeep certainly does this but it's quite obvious when its happening as it sounds like pressure releasing and happens everytime. Also, its only occasional on mine. Most of the time she's quiet but I was polishing her one afternoon and parked in the garage to get out of the rain. Initially I had the radio on, but when it switched off (on timer as the keys weren't in, so 15 mins at least after I switched off), I could hear what sounded like an electrical buzz from somewhere under the bonnet. I did lift the bonnet but I couldn't pinpoint it.
Could be the SBS I guess as I was opening and closing doors. Anyway, I've no complaints and if she need to buzz occasionally that's fine with me!

 

[davidC200K]

Mine has done that since I got it. An kind of electro-mechanical humming noise which appears to come from the passenger side dash somewhere. Goes on for about 15 minutes after the car is stopped and the key removed.

 

[Rory]

The fan in the COMAND unit (and maybe the standard units too?) does that.