I bought a used mariner 12.5 and put it on the water yesterday. When I pedal, the drive makes a humming sound and if I try to pedal moderate or hard, it sounds like the prop is hitting something. Is this normal? I really hope not. I'm hoping that someone will tell me that the previous owner was a liar when he told me that he maintained the propel drive and I just need to take everything apart and grease it up real nice. Does any of this sound familiar? Is it just a maintenance issue?