Note: The following will be fully accurate if you're running TD3.
1. Go to the events tab.
2. Click New event.
3. Create a new event from scratch
4. Enter a description that's easy for you (When the second level begins, for example)
5. Trigger: A level starts
6. Conditions: roundNum=2 && isRound=1
7. Click on New Action.
8. Select Play Sound, and choose the wav file from the drop down box.
If the wav file isn't part of the sound library for TD, you'll have to add it first.
Testing via the dialogue box, I wasn't able to get the test to come back TRUE... however, I ran a mock tournament, and the test worked. If you have further issues, reply back and I'll see what I can do.