I did a google search on snakes of Tennessee and got this website:
None of the venemous ones look like the snake you describe. Click on the pictures and see if you can narrow down which snake you've got in your garage.
Also, if you want to remove it, I would not attempt to do it yourself if you are afraid of it biting you and if you don't know anything about them. Call animal control, they should be able to remove it for you.