I arrive in Nashville at 930am. The rest of my group doesn't arrive until 3ish and we can't check into the rental until 4pm. Any suggestions where I can store my luggage so I can explore on my own for a few hours?
A friend of ours, their daughter will keep your luggage for you. Check out Errands by Erin.
The Downtown Nashville Hostel has just started offering this service as well. It is a VERY nice facility in a great location--downtown on First Avenue N. If you're staying downtown, you could roam Lower Broadway and other landmarks, then return to the hostel and (depending on how much luggage you've got and where you're staying) walk to your hotel with your luggage.
The Downtown Nashville Hostel needs to update their FAQ's: Here is what I just found on their site:
"Can I store my bag at the hostel if I'm not a guest there?
Unfortunately, no. We have so many guests staying with us that we cannot look after the belongings of people who aren’t staying in our facility."