Del Studio 1555 randomly beeps

I have had this computer for ~9 months and recently it has started randomly beeping during normal operation (the kind of loud beep that comes from the BIOS).

It happens every 20 minutes or so, sometimes more often, sometimes not at all. My guess is that this is either a warning about the hard-drive or overheating, but there are no error messages. AFAIK, there are no diagnostic utilities included with the computer that I can use to monitor temperatures & fan speed, or the state of the hard drive. Is my HD going? Should I try to clean the fan with compressed air? So far, it hasn't locked up and I haven't experienced any data loss, but I am very worried.