Why is my Hard Drive Clicking?

Every hard drive has a read-write actuator to input and interpret data from the disc. The actuator scans over the hard drive's platters either reading or writing that data. ... And, in most cases, this is what's causing your hard drive noise. Its very similar to a record player. Imagine the needle moving back and forth. What happens is, the heads on the actuator arm are trying to read the disk and they move back and forth hitting the limiter. This is what causes the clicking sounds. Click, click, click click as it moves back and forward hitting the limiter. The heads are trying to read but because they can no longer read the surface they just loop back and forth. Usually most drives will spin down after multiple read failure attempts. Therefore you would hear the drive spin up, click click click then spin down.