Using a doc camera

I teach online courses at a community college, and when conducting synchronous classes, I often use both my webcam and document camera. To share my document camera, I select it from the "share" option under advanced settings. However, after about two minutes of using it, I hear an audible dinging sound. This forces me to stop sharing and restart the share during class. Is there a setting I may be overlooking to prevent the dinging and avoid having to restart the share every few minutes?