I have a 2007 Mercedes e350 4matic. The car is making a knocking sound when I'm trying to start it. It does have a burning smell coming from the bottom. I can turn the motor by hand. The oil isn't black and it doesn't have a burnt smell. I purchased the car in 2016 and II'v never put a starter on the car. Some mechanics said it's the starter. I say it's the motor. Have anyone else had this problem?

 

lets hear a sound clip while trying to start it. Does it make a knocking sound after its started?

 

It won't crank up. It be trying to but it keeps making that noise. I'll record it tomorrow and let you hear it.

 

That's the starter solenoid failing to engage. Replace the starter.