Other than the noise, if your computer starts (cold boots) in its usual time, without having to wait for the drive to overcome “stiction”, and if programs run normally without hanging up at load time, and if other data loads in normal time, and if, as others have said, the noise is constant, then it probably is fan noise.
But if you have any of the issues that I mentioned first: slow booting, slow program or data loading, then it may very well be a hard drive problem.
What kind of computer do you have that can’t do backups? Not even to CD/DVD drive? External USB drive? Floppy disk? Via serial ports?
PS: Computers are always getting ready to crash. That’s why you need backups even when they don’t “sound funny” and “act weird”, because sometimes they crash with no warning at all.