Inside the drive the heads fly over the platters on air, a few nanometres up, and park on a ramp beside the platter when the drive is off. A drive dropped with its heads parked takes the shock in its chassis, its case and its board: sockets shear, bridge boards crack, and the mechanics usually survive. A drive dropped while spinning has heads in flight over a surface moving at seventy miles an hour at the rim, and the impact pushes them into it. The heads bend, the surface scores, and particles from the score spread across the platter.
That is why the first power-on after a running drop matters so much. Bent heads cannot fly; they drag. Stuck heads are torn free across the surface. A scored platter sheds more particles under a head that is still trying to read it. The click you hear is that process. Every subsequent attempt widens the damage, and by the tenth attempt a drive that was mostly readable has a ring in the platter where the files used to be.
On the bench a dropped drive is opened in clean air before it is powered, the heads inspected, the platters checked for contact, and the heads replaced with a matched set. Then it is imaged once, head by head, with any scored surface read last and slowest. Where the fall took the case's socket or bridge instead, the repair is to the board and the drive is often untouched.