I have two laptops running Ubuntu 7.04 (Feisty), both kept up-to-date
using the update manager, but installed at somewhat different times
and with slightly different packages (due to how they're used). Both
are using the default GNOME desktop.

On one I have the ability to hover the mouse over the icon of an MP3
file in the file browser and it'll put a little music note above the
icon while it plays the preview. On the other this does not happen.

Both have the libraries needed to play MP3s in various players (gxine,
Rhythmbox, etc.) and both are used frequently to play and create MP3s
to be transferred to portable MP3 players. Both have the "preview
local audio files" option chosen in the settings manager.

What set of packages or configuration options is the second laptop
missing that the first must surely have to enable this feature? The
second laptop is my kid's, and is used even more often on audio files
than my own is, so enabling this feature is desirable.