Recently I started hearing a strange "plastic-like" knocks right after starting the engine.
EDIT. Here's the video: http://www.youtube.com/watch?v=i4mLn_-nUYA
I also tried it with the engine off (not filmed), and the knocks are still there. Interestingly enough, when I turn the engine on, hear the knock, and turn the engine off, I do hear the knocks and a very faint noise in the background. When the noise stops, the knocks stop as well.
Knocks seem to be coming from the heater but I doubt whether it's truly the heater. The sound goes away within about a minute or so. If the car is warm it's even faster - about 10-15 seconds.
The car -
Mercedes C180 Kompressor. Any ideas what it may be?