My Parents 2012 500 TwinAir has done this since a couple of months old. Does it whilst the starter motor is turning and then for a fraction of a second after the engine fires.
It sounds rubbish but the dealer couldn't find anything at the interim oil change when we asked them, and nothing untoward was spotted at the main service in April so God knows. Might be alternator perhaps. I gave up because I could see it'd turn into several trips back and forth to the dealer and lots of head scratching, as is usually the case when something breaks these days - no one actually knows unless a computer tells them!