The screen saver After Dark v. 2.0, runs silently if HyperCard is the
application that's open when After Dark kicks in. This is because
HyperCard takes control over sound while it is running.
After Dark, v.2.0u (for System 7) may also cause the cursor to change to
After Dark's "never sleep" icon. This has been reported to Berkeley
Systems.
additional search term: AfterDark
This article is adapted from the Claris Tech Info database.