I have '09 C350 appx 7000 miles.....morning cold engine start (ambient temp appx 65 deg F) I will hear a somewhat unusual sound - - low pitch "growl" in front crank area----it will last for a minute or two----then goes away. Oil level normal and no messages/lights/etc. Anyone else experience this please? Thanks for your review Love the car!....Ralph Tucker

 

I am almost positive my car has that same sound on startup

 

could be a normal thing but i dont have that, granted my car is in the garage, but to be sure u should take it to the dealer and have it looked at just in case.

 

On a cold start, all modern engines are doing everything they can to get the cats as hot as fast as they can to reduce emissions - a cold engine pollutes alot, until the converters warm up.