Creepy noises reported as being heard from within computers, their causes, and possible cures:
Grinding or moaning, constant or intermittent: This is one of the most common noise problems in computers. It can usually be traced back to a defective cooling fan, usually the one on the CPU Cooler. Smaller fans tend to fail more often, especially if they're cheap sleeve bearing types. See Grinding power supply fans and how to fix them.
Rattling: Check for loose screws on the case. This is usually a removable side panel rattling on its mount. Applying masking tape over the edges of the case where it contacts the cover may cure this. Beware: Some hard disk drives may rattle when they're beginning to fail. If the problem is coupled with occasional "Hard Disk Not Found" (or whatever your BIOS uses in place of the old IBM error 1701) error when starting the system up, you may need to replace it soon.
Assorted noises right after inserting or accessing a CD-ROM disc: If you get a loud buzzing, the CD-ROM drive probably isn't screwed in as well as it should. Do not tighten the screws too much, or the tray may jam. If you're getting noise similar to that of rolling surf, or rain falling on a roof (quite pleasant, really) whenever the drive starts or stops, it may be equipped with a vibration damper in the spindle motor, containing loose material of some sort that shifts around - if your drive is one of these, it's much less likely to buzz or generate read errors with an unbalanced disc.
Squealing: This is common on very old hard disk drives. There is a small copper grounding terminal, known as a static brush, with a graphite tip which rides on the rounded tip of the spindle motor shaft, on drives which have the spindle motor outside the sealed HDA enclosure. Over time, the graphite tip wears down, and will vibrate, producing anything from a piercing fingernails on a chalkboard sound to a rattle. The solution to this is to take the drive out and apply a piece of double-sided tape to the back of the static brush. You may also be able to fix the noise by bending it slightly so the shaft tip rides on a non-worn section of the graphite button. This same device can be found inside some VCRs, and is known to exhibit the same problems.
Moans from within the machine, indicating a desire to consume the brains and/or flesh of helpless humans: RUN. | 
