Fixed system "bell.oga" sound sometimes playing instead of Windows 7 bell sound

Fixed system sound "bell.oga" (/usr/share/sounds/freedesktop/stereo/bell.oga) playing in certain instances instead of the Windows 7 bell sound.

In each sound scheme, I copied the "audio-volume-change.wav" file and renamed the copy "bell.wav" which fixed the problem.

The only example of this problem happening that I can think of off of the top of my head is hitting Ctrl+F in Firefox and typing something that isn't on the page.