To find out if the hard disk drive is causing the strange noise, disconnect the drive's power cable before turning the computer back on. After you turned on your computer (this time the power cable of your hard drive is disconnected) and there is no more strange sound coming from your computer, that means there's a problem with your hard drive.
If the hard drive is the noise source, your next step is to download a utility that can read the SMART (Self Monitoring Analysis and Reporting Technology) diagnostics codes off the hard drive. SMART data can tell you exactly what's wrong. Here's some of the link to drive's SMART utility download page.
IBM(Hitachi)Another thing to consider are the fans in your computer. If you are concerned about an unusual fan noise, you can use some utility for monitoring your computer system temperature. You can use the free SpeedFan Tool to see if a cooling fan attached to your motherboard is spinning too slowly.
FAQ: Low level format
digital temperature sensors is really useful. If you are trying to figure out why your pc hangs when under heavy load or after some hours of usage, SpeedFan might help you to find the real cause. Very often it is a poor power supply, or an improperly installed heatsink that lead to behaviours that we tend to associate with errors from the operating system, but that are not. SpeedFan automatically searches your computer for interesting chips: the hardware monitor chips. SpeedFan can expose voltages, fan speeds and temperatures.Some parts of your computer will fry themselves if not cooled, and a new fan costs far less than a new CPU or Video Card. So please maintain your PC by cleaning it regularly and by keeping it strange noise free.