3T G-Tech Drive Causing beachballs

I have a 3T G-Tech drive attached ot my 27" imac (prevoisuly used with 21" imac) I use it for Time Machine only. Time machine is currently turned off. For some reason the drive still spins up occassionaly(not sure why it is doing this if TM is not running) and I get the beach ball for 15-20 seconds. The drive was doing the same thing with the old imac so I don't think it has anything to do with connectivity. (was Firewire, now thunderbolt to firewire adapter) Any ideas how to stop this? It happens when I am in the middle of editing a photo or writing...and I just have to wait.

ANy suggestions for stopping this?

Thanks,

NJ