I have an iBook G3 700 Combo Drive 648 megs of RAM and a 20 GB hard drive. Every now and then specifically when I'm running high processor tasks, the hard drive makes this wierd noise, which is a sequence that repeats over and over again. I can't tell if it is writing to the disk or reading from the disk. It makes 3 short noises, and then a long noise: (short - short - short - long) Try to imaging that noise. It is just the sound of the hard drive working. This will repeat itself over and over. Sometimes If I have lots of tabs open at once in safari and i open them at the same time that will happed. But after like a minute it will stop. But other times it will keep repeating that noise over and over for ever so I have to manually restart the computer forcefully. (Holding down the power button) The computer also freezes and I get that spinning color wheel. I dont know why this is happening. Thank you for your responses!!