Co-host's audio is coming across really distorted.

I am hosting a webinar. It's a play reading. I have asked the co-host to run the sound effects, which are streaming off sound effects websites.  When we rehearsed, the sound effects sounded fine to her, but they were coming across  hideously distorted on my computer. I am assuming that all the attendees will also hear them distorted. Why is this happening and how can I fix this? Thanks!