I've had my slingbox classic for years now. It has been working fine, with clients on windows, osX, and web browser. Something happened about a week ago. I can connect to my slingbox, picture is fine, but slingbox drops sound after some time. Sometimes it is almost right away, sometimes it is few minutes. I tested connection via different cables, also network side, clients on various PCs, also reset to default values and reconfigured. When I switch into "Setup Assistant", I can get sound going for some time, but even in Setup Assistant sound is dropped eventually. I also tried wired connection instead of WIFI from PC, same story. I did not go through any firmware upgrade recently. Other than an issue with my slingbox hardware (memory, ???), I can't think of much else to check.
It seems that you are having some issues with your Slingbox Classic audio signal.
Most of the times, the audio issues are related to network connections. With this in mind, I recommend you to check this link: