The answer to 'why is my garbage disposal constantly running' is that the disposal is likely stuck or jammed, causing it to run continuously. This can happen if a foreign object gets lodged in the disposal, the blades are dull or worn out, or the disposal's motor is malfunctioning.
Some common symptoms of a constantly running garbage disposal include a humming or buzzing noise, the disposal not turning off when you flip the switch, and increased water usage. To troubleshoot, first try to clear any jams by turning off the power, inserting an Allen wrench into the bottom of the disposal to manually spin the blades, and removing any trapped objects. If that doesn't work, you may need to replace the disposal or call a professional plumber to diagnose and repair the issue.