Pure Sine Wave click sound

I was recording the Pure Sine Wave output to create a file to hum along with, and discovered that when 8 or more sliders are all highlighted (with the Ctrl key) that the output will have a click sound every 30 to 60 seconds lasting only a second.  When I zoom in on the recorded file, it will show a flat line (gap) in the audio during that moment.  It might be an interrupt from Vista taking priority over the audio, however my other audio applications produce and record sound (much longer than 60 seconds) without having a gap or click in the audio. 

Again, this might just be my computer, but I thought I would mention it in case it is a bug.  To reproduce the problem: highlight 8 or more harmonics and let it play a sine wave for 60 seconds and listen for a click sometime during the minute.  The time interval of the click varies, but will occur somtime within a minute.  I tried recording with Sound Forge and Sonar and it happens with either.  My soundcard is a Creative SB X-Fi, and the recording method is "What you hear." 

I have written a few audio apps before and found this type thing can happen when playing audio without a "double buffer" method when feeding the raw data to the soundcard.  However, let me say this application is very well written and is very useful for studying overtones.  This is just a minor issue in an otherwise exceptionally great software program.