Make a recording - yourself, your friends, a song, the TV - whatever you can see that makes a noise. Then play it back in reverse!
You can even change the playback speed. Make yourself sound like a chipmunk after three cups of coffee, or an extremely tired sloth.
Save your favorite sounds and rename them to make it easy to keep track.

Try out these two phrases - record them and reverse them: "No Worries" and "Zero One". Amazing isn't it!