The heating, ventilation and AC (HVAC) heater box is susceptible to mildew buildup. This can result in a musty odor from the HVAC system, most noticeable when the system is first turned on.Google+
Car Problem Reports
Mercedes-Benz C280 4MATIC Mildew in Heater Box
Mercedes-Benz C280 4MATIC Problem
Average Mileage: 44,333 mi (23,000 mi - 72,000 mi)
Visitor, 2007 Mercedes-Benz C280 4MATIC, 72,000 mi
mildew almost wet shoe smell when heat turned on. Replaced part in hvac system over all happy with the vehicle. We call it the snow commander. Worried about the cam shaft issue many report. No check engine light yet but it seems MB would be right to recall the vehicle due to such a prevalent issue.