Hi Katie,
It could be a demo plugin injecting a beep into the audio stream or some other factor. Things like this are difficult to troubleshoot from a distance with so little information. If you are hearing a regular beeping noise and can't track it back to the demo version of a plugin or something similar.....
1. File > Save to New Folder to save the song and post that entire song folder where it can be downloaded, DropBox, etc.
2. Make a support ticket explaining what's happening and link to where the support rep can download the song that exhibits that issue.
