My Passport (constantly running?)

I have a My Passport for Mac and I was curious if it is SUPPOSE to be running all the time when plugged in (I can feel it vibrating).  My Time Machine backs up every hour but it seems to run the entire time it is plugged in.   Is this normal?  Or should I not keep the My Passport for Mac plugged in?  (I just thought it was easier to keep it plugged in and let it do its thing…I also have a laptop I will occasionally disconnect backup using this hard drive).

Thanks for your help in advance!

you can eject the drive as soon as the backup is done

it should not be running unless a backup is in process