Last night my car sat outside for 3.5 hours at -29 while I was in a meeting. (the C230)
When I started it (unplugged) it most definitely did NOT sound like a diesel. This is not normal.
The M111 mill is not the quietest engine made, but not THAT noisy.
Other than confirming this is not normal, I have no solution, as it is too hard to tell you something without:
1. Where is the noise coming from?
2. How long does it last?
I can tell you this will be practically impossible to diagnose via this forum. You will need to have a tech replicate the problem.
1998 C230 "Black Betty"