SONAR takes forever to scan a file

Can anyone tell me why it takes so long for SONAR to catch a file and bring up the pop-ups? I am running NIS 2010 on an old P4 2.8 GHZ with 2 MB memory and when SONAR catches a file, it can take up to 20 seconds or more before I ever see a pop-up. It should work a lot faster than that.