you might want to turn your computer into an audio OSCILLOSCOPE !

Several ways you can do this:

MacIntosh Shareware Programs

IBM PC Shareware Programs

Sound Sculptor Spectra
Digital Oscilloscope Sound Effects
SoundView

Java Programs
Java Synthesizer: http://zerius.victoria.bc.ca/synth/
WaveView: http://www.ldc.upenn.edu/lol/greeting.html