Whirlpool Bottom Drawer Freezer Frosted Over

I noticed two days ago that my food in the freezer had a little frost on them. After noticing this it seemed to me that the unit was running louder and more often.

This evening I opened the drawer to take something out and found that everything was frosted over with icicles on the light cover and ice everywhere. No water on the floor, though, and the refrigerator is keeping things cold. I pulled everything out of the freezer and put them in another freezer. I plan to unplug the unit tomorrow and clean out the ice.

I found that there was a large amount of dog hair behind the bottom face plate that appears to have been clogging the bottom coils - I have two large dogs - so I vacuumed it all out well. It seems that the unit is running quieter and not as much now.

Is there some diagnostic that I should run to see if the unit is running ok?

Could it be that I didn't shut the drawer all the way a couple of days ago and it caused the icing? Still, this wouldn't answer why I noticed the frost then. I didn't notice if the drawer was slightly open when I found the problem tonight.

Thanks,
Ken