How long since you opened the case and cleaned it out? Buy a can of air and a anti-static strap from Walmart, BestBuy, CompUSA, etc. to blow the dirt, dust, etc. out of the inside of the case and reseat all your components. Dont touch anything in the case unless you wear an anti-static wrist strap (recommended) or maintain contact with the case chassis before and during reseating. Get down near the components, and listen for the source of the sound.
Could be your CD-ROM, remove any CD located there. Could be your Hard Drive going bad, back up any important data, drive may be close to dying. If for sure it is the drive, go ahead and purchase a new drive, then copy all important info from old one (as slave) to new one (as master). May I suggest a drive for you? Western Digital 80GB with 8MB cache. Look to Newegg.com for best prices and service.
Could also be fan going bad (spinning up, then hanging, spinning up again, etc.). If it is a fan on your processor, dont run the computer until you replace the fan, as overheating can ruin the processor and mobo. If a case fan, just replace asap.
<font color=blue>TNguy</font color=blue>
Information Technology Instructor<P ID="edit"><FONT class="small">Edited by tnguy on 03/22/03 13:03.</FONT></P>