Do you have any old CDs laying around?
If you have used the Amazon Trade-In Program in the past you're familiar with the service that allows you to trade in things for gift card credit. Apparently, Amazon has added an option to trade in used music CDs as well. However, it seems on the option is there, the CD trading mechanism isn't functioning right now.
There is no indication of how much Amazon will give you for used music CDs, but it's likely the only be a few dollars if they are in perfect condition. There isn't much value and used music these days considering most people buy digital. I'm rather surprised Amazon is even doing this.