Any ideas what this attached sound could be?

I usually hear the sound (maybe ticking, clicking,...) when I first start my car (2003 c240 W203). It tends to last maybe thirty times before going away.

 

Is this sound taken from the inside of your car? Maybe sounds like somewhere in the dash?
If so it sounds to me like the steeper motors that move where the air goes and other functions of the HVAC system in the car.
Check out this thread https://mbworld.org/forums/c-class-w...g-hissing.html
"To normalize the A/c stepper motors, hold down the Recirc and Front windshield buttons for about 10 seconds or until they both start flashing back and forth. When they are done flashing and you have confirmed everything is working, you are done."
When the noise goes away run this and if your systems is working correctly it will stop... If you hear the noise and it never ends the test that may be a good place to start.

 

That is the famous stepper motor. Welcome to the club. Either the motor gears have stripped, or the linkages have snapped. Or both.

The linkages for your car have been updated with beefier versions. The dealer will also have a single kit PN that contains a bag with all of the updated (2?) linkage arms. Kit PN is A203-830-00-33.

For some reason, the linkage and motor that control the airflow damper for the driver's side footwell (L side on a LHD car) always seem to break first. That would be my guess for your situation. Change out every (both?) linkage available in the kit. Do not skimp out. I had mine done under warranty so cannot confirm what was inside the bag itself.

When I opened mine up, I found the gears for the corresponding motor were stripped as well. The electrical part of the motors do not fail. The dumb part is that the gears cannot be purchased separately (not that I know of at least) as they're sold as a complete subassembly. Therefore you're also looking at a new motor which contains all the gears. Again, do not skimp out.

Some people have opened up the motor assembly and rotated the gear to a "good" part then put everything back together. I don't recommend this, as there's no guarantee that this will be done properly based on the range of motion. The last thing I want to do is open up half the car again just because I set the gear angle incorrectly or it turns out there was something else wrong with the motor assembly. Trust me, you will hate yourself while doing this job. I've had to do this job twice (ie 2 different failed motors). In each case it was a different internal gear that failed.

The PN for the stepper motor is A203-820-16-42. There is no updated version that I know of.

Opening up the dash to get to the individual motors is a real pita as you will soon see. Because of this, you may want to consider swapping out more than 1 motor unless you want to do this job multiple times as the individual motors fail one by one. Most mechanics will replace all of the motors in one shot because of the work involved. Your car (C240) has 6 motors in total.

The good news is that the lower L motor is the most accessible of the 6. It requires removing the least stuff, which is still a whole pile of parts. When my defroster motor died (the least accessible motor of the bunch) I had to remove the glove box and upper dash as well. That was a fun time.

Good luck.