If Ad-Aware's obnoxious "target found" sound drives you insane, switch to something more to your liking.
Just click the gear-shaped Settings button, then the Interface button on the left, then the folder next to Play This Wave File if Targets are Found, and browse for another sound. You can use anything that is already on your computer. Almost anything would be an improvement.
You can find many different .wav samples on the web, just try searching google for something that is more to your liking. I personally use Homers most famous quote from the Simpsons.
Alternately, you can turn off the sound completely by going into Settings, hitting the Tweak button on the bottom left, and choosing Misc Settings and Play Sound.