I was out fishing tonight and getting no bites so went for a cruise. Was doing 20mph in my ranger r81 with 150hp 2 stroke yamaha vmax. I was easing off the throttle and slipped it into neutral quicker than I wanted to. In any event, when i shifted into gear the rest of the night the outboard made a clanking metall noise. It ran fine but wondering what the heck did i do to my motor and is it it a big repair or simle fix.

Pulling it out of gear shouldn't have done anything to it. Does your prop spin freely and without noise when out of the water?

Yes, no problem at all with the prop spinning. I thought I might have damaged the gears from pulling it from gear to neutral so quick.  I trailered the boat to work today, so going to see if the noise is still there today. 

Usually if you have damaged gears in your lu you can hear them when you turn the prop, or at least in the ones I've seen anyway. As far as I know, pulling it out of gear shouldn't do anything as it's not locking anything up, but allowing it to spin freely as water passes by. Hopefully everything checks out though.

If it's only making the noise when it's in gear, then that comes pretty close to saying the problem is in the Lower unit.  If it's making the noise all the time, not being able to hear where it's coming from myself, and if you can't, You might want to look at pulling the lower unit off and starting it up without it.  If the noise is still there, then you know it's something in the powerhead, if it's gone then it's probably the lower unit.  You can run one for 20-30 seconds or so like that, but no more without giving it a long time to cool.  The drive shaft can transmit noise from the lower unit up to the powerhead and make it sound like the powerhead has a noise.

Just to be clear- their is a single metal clang going from neutral into gear. Then the noise is gone. 

Motor ran fine tonight. Fingers crossed.