What I said above. That's the issue. Your bed NEVER goes down. The arduino thinks it is constantly hitting the Z limit switch. You got some junk down in there I think. Clean it out. Problem solved.
I mean it goes down after hitting the head very hard but that's because it's moving very fast then and the steppers can occasionally go the wrong way if they are being pulsed fast enough and you shove them the wrong way to get going. So ignore that. Basically it is SILENT every time it should be going down.
That is exactly what you expect when the limit switch is stuck in the down position.
Thank you so much this fixed it!