Mercedes will not start

My Mercedes Benz C250 started making a growl
and sputtering noise when starting. It was worsr at  
the beginning of the day but lessen later. Imagine
cold start worse. A week later and now the car
clicks and will not start. Yet if I try 3 more times or
on the forth its starts with the growl and then no
problems. Last message on the car was a
crankshaft sensor that was changed. And no other
mechanical issues other than regular
maintenance. A friend mentioned could be a
secondary consumer battery or that start motor
breaking but not yet. My confusion is that I notice
the acoustic alarm when closing and opening the
car is weak. And turn off consumables seems to
make start faster.