What tool is used to change the motor drive/pump coupling when it is noisy?

The use of a 1/8 inch Allen key wrench is appropriate for changing the motor drive/pump coupling when it is noisy because many pump and motor couplings are secured with set screws that require an Allen (also known as a hex) wrench for adjustment or removal. These couplings are designed to accommodate various types of connections, and Allen key wrenches provide the necessary grip and leverage to securely loosen or tighten the set screws, ensuring proper alignment and function of the coupling.

This tool's design allows it to fit snugly into the hexagonal recess of the screw, reducing the likelihood of stripping the screw during adjustment. The other tools listed, such as the flathead screwdriver and the Phillips screwdriver, are not suited for this task as they are used for different types of fasteners. A socket wrench, while useful for other types of nuts and bolts, may not fit the specific set screws typically found in pump couplings, making the Allen key the most effective choice in this scenario.