G-Tech G-Drive Thunderbolt 4TB

G-Tech G-Drive Thunderbolt 4TB is clicking while strolling and then the new Imac crashes and automatically reboots?

I purchased the G-Tech G-Drive Thunderbolt 4TB was purchase on December 14, 2016 from Apple Friendly Center in Greensboro, NC. It worked fine on my MacBook Pro. Then I puchased a new Imac in February. Now the Thunderbolt is clicking when I scroll for files and all of a sudden the external drive starts to click while scrolling and then the entire system crashes, but will reboot automatically. This happens constantly. What is the problem??

Morris Davis