Ski Nautique 2001 grinding noise

ok, so i bought an 1982 Ski Nautique 2001. I took it to the lake today and it was running great, cranks up everytime very easily. I rode it around for about an hour, and when coming back in when i switched it to neutral it makes this grinding noise, exactly the sound of grinding gears in a standard truck. It only makes this noise in neutral, not forward or reverse. Anybody have this problem or know where i need to start?