High Pitched Sound

My iMac has produced a high pitched sound from time to time since the time I bought it. However recently I have noticed that together with this high pitched sound, the programs are also "hanging". As soon as the sound goes away everything starts working again.

The applications does not always hang when the sound appear, but the sound is always there when the applications hang.

Is this a hardware or software issue? Does anybody know what is happening? What can I do to make it stop?

Please help!


Hardware Overview:

Model Name: iMac
Model Identifier: iMac7,1
Processor Name: Intel Core 2 Duo
Processor Speed: 2.4 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache: 4 MB
Memory: 1 GB
Bus Speed: 800 MHz
Boot ROM Version: IM71.007A.B03
SMC Version: 1.20f4

System Version: Mac OS X 10.5.5 (9F33)