sound dropping out when streaming

For the last week or so, the sound drops out off and on or goes out completely. I chatted with customer support and they said the problem isn't on Xfinity's end as he checked the speed and it was good. However, this happens on both tvs, on all apps I stream (Netflix, Hulu, You Tube). His solution was to send me an upgraded modem for an additional monthly fee. He also suggested contacting customer service for the problems with my apps. The common denominator here is Xfinity. I don't see how the problem could be my tvs, or the apps. I am trying to get this fixed one more time before looking for another Internet provider.