My thought is that there is some power saving function kicking in after noting "x" minutes of inactivitiy.
E.g., no keyboard or mouse actions. You just put on the earphones, sit back, and listen. (And maybe snooze away....)
Try timing the pauses to see if the time is consistent. Then look for a matching configuration within power saving settings.
Another thing you can do is use a third party utility tool to simulate mouse movement. Then the "power saver clock" is restarted.
I have used "Mouse Move" in the past to do just that....