What are these big green or gray balls falling from my tree that bang on the roof?

Black Walnut. They are dropping now.
Here are some pictures

You can eat them but it is a lot of work and you have to get to them before the squirrels.
I have a junk set of golf clubs and enjoy whacking them out into my woods with a 5 iron. It is really fun.

I have a tree with the black walnuts @worriedguy has pics of. Keep your kids away from them or the squirrels will attack. :-)

I have a 1970 Barracuda stored in my barn. Two years ago I went out there and found the floor, seats, and rear deck covered in black walnut husks at least 4 inches thick! Disgusting!
That is when I declared war on Rocky and his friends.

thanks!!!
A Barracuda! Waiting for Barrett-Jackson?? My dad had one in olive green and sold it cheap. Real fast, white leather.
I hate this tree.

The Grinch stole Christmas a little early?

It is a messy tree and puts out juglone which kills other plants nearby.

Yep. I am the original owner. Rocky, Chip and Dale, and Mickey have not been around this year.