The Cause of the Clicking
Iomega Zip and Jaz drives cause Click Of Death by incorrectly writing to their removable media. This miswriting can damage the user's data, the factory-written low-level formatting, the head's positioning servo information, and the proprietary "Z-Tracks" that are used internally to manage and maintain the Zip and Jaz drive's cartridge data.
The clicking sound itself is nothing more than the sound of the heads being retracted from the cartridge into the drive then immediately reinserted. This deliberate strategy is employed by the drive when it is having trouble locating, reading, or writing any of the cartridge's data. This removal and reinsertion of the heads recalibrates the head positioning mechanism, "scrubs" the heads to remove excessive oxide deposits, and eliminates electrostatic charge build-up on the heads.
It is VERY IMPORTANT for you to understand that the clicking sound itself is NOT the problem. The clicking is just an audible indication of a drive that is having trouble accessing the data on a cartridge.
So for example, if a cartridge that was clicking in one drive is inserted into another where it also clicks, this DOES NOT MEAN that this second drive has now been somehow infected by Click Death. It only means that the damage that was done to the cartridge -- probably BY the first drive -- has now made the cartridge unreadable by any other drive, which will also "click" as it tries to access the damaged cartridge's data.
Incidents of Click Death have been linked to bad external power supplies, loose power connectors, excessive magnetic oxide build-up on the drive's heads, magnetic and radio interference from nearby sources, media damage from excessive wear or mistreatment, and a seemingly endless array of internal electrical and mechanical problems from causes ranging from excessively rough handling of portable drives through defective original manufacturing.