Mike, you nailed it. My metronome wasn't set to output anywhere. In case anyone else has the same issue, here are the steps to fix it:
1. Go to Edit / Preferences
2. Select Metronome (in the Project section)
3. Under Audio Metronome, there are three settings: First Beat, Other Beats, and Output. Check to make sure that Output is not set to None
Thanks!
- Bret