External Speakers not working on Dell All-in-One 7480 & 7490

These are Windows 10 PCs. They are Dell All-in-One 7480 & 7490. When external speakers are used, there is no sound. 

The PCs are new and have been tested. The speakers work if Zoom is not being used. Zoom client was manually downloaded and installed on each PC to ensure that the most current version was used. However, when Zoom is being used, the speakers do not work.

Dennis Caldon