Multimedia Playback
If the framebuffer of the graphics controller is not updated, the picture of the computer screen will appear to hang until the buffer receives new data. Many video player programs (e.g. MPlayer) feature the ability to drop frames if the system is overloaded, intentionally allowing a buffer underrun to keep up the tempo.
The buffer in an audio controller is a ring buffer. If an underrun occurs and the audio controller is not stopped, it will keep repeating the sound contained in the buffer, which may hold a quarter of a second. Such effect is commonly referred to as "machinegun". This happens if the operating system hangs during audio playback. An error handling routine (e.g. blue screen of death) may eventually stop the audio controller.
Read more about this topic: Buffer Underrun