Use of digital/optical output on mid 2010 iMac causing occasional popping sound

I've been using the optical output of a 2010 iMac 21.5" Core i3 3.06 GHz for a handful of days and am trying to hunt down a popping sound problem.

I am using a mini toslink adapter on a standard toslink/adat cable to connect to the iMac's headphone/digital out jack and go into a digital toslink to analog RCA converter to achieve this. I really love the sound. It's virtually noise-free compared to using the straight up analog output of the iMac where you can hear digital noise because of grounding issues when you really turn up your external speakers. So I prefer the quiet and clean digital output.

However, I'm noticing that every once in a while I hear a quick POP sound. It's only a handful of times a day so it's not all of the time and I'm seeing it on both Mountain Lion 10.8.5 and Mavericks 10.9.5.

It's entirely possible that the problem could be the optical to RCA converter I'm using, but since I don't have a different one to try, I can't test anything else with the iMac's optical out to rule the external converter out as the culprit.

The only thing that my internet searches have yielded is that some people have reported this online in various forums as well, and some responses are that the digital iMac's audio outputs go to "sleep" sometimes when they haven't been passing sound in a while and the act of going to sleep is what causes this.

I found that back during OS X 10.5 Leopard apparently someone created a program called SoundStay that would play a blank audio file all of the time to stop the digital output from going to sleep. But it hasn't been updated in forever and I don't want to try it on 10.8 or 10.9.

And I also want to see if I can confirm that this is really what is happening and also want to know, if so, what other people can do about remedying this issue these days with newer iMacs.

Thank you for anyone who can share direct knowledge/experience of this issue.