iMac making a sound i haven't heard before

can somebody tell me what this sound means, where to find it? http://seankelleys.com/media/mp3/water-drop.mp3

i recorded the sound with soundbooth and named it water-drop.mp3, that's not the real name

i've looked in the libraries through the sounds, nothing there

my applications http://seankelleys.com/media/images/10-01-11-applications.png

i was hearing the sound before installing the adobe products and iLife '09

i don't remember hearing this sound as long as i've had my mac, recently i did a disk repair, erase and install, and reset the System Management Controller because of problems with

1. computer starts up fine from pushing button but takes a long time to restart or won't restart at all through the upper left apple () > restart, when i try restarting i see the white screen (screen before the grey apple shows up) and grey apple and loading circle never show up

2. after using an application other applications won't work or are very slow and i have to try restarting3. when working with more than one application and going from one to the other they'll take a long time to switch application windows usually rainbow wheel will show up or the application will freeze up with rainbow wheel appearing4. problems quitting applications, must force quit, sometimes force quit doesn't work

5. external devices/drives stop working (window pops up saying device not found) THIS IS STILL HAPPENING

i think I was able to fix most of the problems by resetting the System Management Controller (SMC)

1. Shut down the computer.
2. Unplug the computer's power cord.
3. Wait fifteen seconds.
4. Attach the computer's power cord.
5. Wait five seconds, then press the power button to turn on the computer.

iMac info

iMac (20-inch Late 2006)

version 10.5.8 - Leopard

processor 2.16

memory 3GB 667 MHz DDR2 SDRAM

Macintosh HD

capacity 232.57
available 152.57
used 79.78

any help is appreciated,

sean k