I have a machine running XP Pro and a Creative Labs Audigy 2 ZS sound card feeding an Altec Lansing 2 speaker system with a subwoofer. The audio out goes into the subwoofer which then has outs for the speakers. Into a second audio in on the subwoofer I also have my Mac Mini plugged in.
When I'm playing audio the sound will just cut out. Sometimes for just a second or two and sometimes I have to click the software volume control. This happens both on the PC and Mac. There doesn't seem to be any rhyme or reason to it, and sometimes it doesn't every couple of minutes and sometimes it's fine for hours.
I realize it's probably the subwoofer/speakers as they are going on 15 years old, but I'm curious as to why touching the software volume control has any effect on it and if there is a possible cure because I'm otherwise happy with the speakers, despite their age.

Could it be a loose connection (or even internal in the sreaker connection?) Touching the volume control could well give a vibration that makes contact. If fifteen years of use can lead to the contacts getting 'dirty' at terminals or loose and thus giving intermittent results.

I change the volume on the screen, not the physical volume control.