you didn't say anything about your OS or your audio drivers but i usually have this problem with Realtek.
Realtek was what I had problems with on my HP. It was misdetecting whether I had a set of earphones plugged in or not and switching modes on me. Enabling that autopopup made it happen more frequently, so I had to disable that.
I'd have to force it to correct itself by actually plugging something in and then unplugging it, forcing it to switch to the correct mode. Funny thing is that was usually the only time I ever plugged in a set of earphones. I didn't have any other use for them except as a Realtek fixing tool.
I'm beginning to think that it may have something to do with my ear piece being plugged into the audio jacks when I put it into standby.
So I think I may just try to unplug them just before I go into standby and see if that sort of solves the problem.
If that works and you forget to unplug them, or that doesn't work, just try what I said, plugging the earphones in & out a few times, because you might be having the same problem I had.
You also said you may have been listening to an audio just before putting the laptop in standby. You didn't say what format of audio or with what software.
I had some sort of codec clash on my old pc when using audio in teamspeak. Everything worked fine in both teamspeak and my whole OS, until I closed that application. Then I would lose all sound till I rebooted. As long as I didn't close teamspeak till I was ready to reboot any way, I didn't have a problem. (that's why I have always hated using teamspeak)
So test whether it's related to running that audio application or with a specific file format first, before you go into standby. Close that application and make sure you still have sound elsewhere (just click the little lever on the Windows volume control to make that little "ding" sound). If you don't have sound, then I would say you have narrowed down the source of problem considerably, and it has nothing to do with going into standby.
If everything still works fine, then try making sure whatever application you use to play audio files is closed before going into standby and see if that helps.