I have a black walnut tree that has a hole in one side that birds were living in earlier this year. It is missing large pieces of bark that looks like it got hit by a car. It also has a crack running around it more than half way. It makes a noise constantly like a pop or a tap. It also creaks. The noise is coming from the hole, crack area. Could it be falling over?

Falling over from the roots? Unlikely. Rotted and breaking off? Possibly.

I would say it needs to come down before it falls down.