long beep accessing drives

When I try to access a cdrom or floppy disk, or even try to run a scandisk, the pc gives off a single extended beep for the duration of my access. I disconnected the speaker cable, but the sound is eminating from the motherboard. I have checked all the connections, checked for irregular software, etc. I have just purchased the components, and all the drive has on it is Windows 98, NAV 2001, Office97, and the video drivers. The machine was fine last night, and nothing new has been added. Any idea what could be causing the beep?