2004 Merc C Class Making Rattling Noise (Not Engine Related)For 30 Seconds On Startup

[lacmag3]

My 2004 Mercedes has begun making a rattling noise from high up behind the dashboard (passenger side) or behind the glove compartment. It happens each time I start the car and lasts for the 30 seconds only. It's not the engine as the noise is too far removed. Has anyone had experience of this?

[ToraToraTora]

most likely it's the timing chain and or tensioner. Ideally should be replaced but unlikely to break.The noise subsides when the oil pressure gets up.

[tonyav]

Sounds like a broken stepper motor to me ( operates heating and air con flaps ) had that happen to me with a Saab I once owned. Could be the linkage on the motor or the motor itself.

[Hopkirk]

I found similar in my mother in law's old Vauxhall Meriva, although it wouldn't stop.

It turned out to be what Tony describes. The button to recirculate air in the ventilation system operated a flap. Normally it should be in position to allow fresh air in, but the motor couldn't quite push it all the way, so it kept trying.

I disconnected power to the motor, and wedged the flap in the correct position.

I then told the mother in law that she couldn't recirculate the air.

It wasn't a problem, as she didn't know what the button did anyway.

[tonyav]

Stepper motor will look like this
http://i.ebayimg.com/00/s/MTIwMFgxNjAw/z/eUoAAOxy63FS8fI0/$_35.JPG

Inside the stepper motor will look like this.
https://mbworld.org/forums/attachments/c-class-w203/292263d1406798660-noisy-air-conditioner-stepper-motor-replacement-clicking-hissing-img_5773.jpg

[ToraToraTora]

my reason for suggesting what I did was that if it was the stepper it would not go away 30 seconds after starting up.

[Hopkirk]

Try operating all the ventilation controls and see if it affects the noise.

[tonyav]

Mine did, it was the climate control going to the temp setting.

[TonyV]

TTT but from description of where noise is coming from " high up behind dashboard (passenger side) or behind glove compartment " it can't be anything engine related IMO.

[ToraToraTora]

fair enough but sounds often sound like they are coming from a place they are not.

[TonyV]

TTT I appreciate that noise can travel but I had no better suggestion, so didn't want to just be negative. But suggestion to OP is if have a long screwdriver, piece of dowel, or anything similar, when noise is occurring, put one end on a component and other end to your ear, you will be able to isolate where noise is coming from. Don't know why I didn't suggest that earlier.

[TonyV]

^^^^
My suggestion just a homemade version of one of these.

https://www.amazon.co.uk/Silverline-154006-Mechanics-Stethoscope-320/dp/B001C0RYPG