No idea, but how about some things to play with?
Disable all the system sounds by going to sound, sounds tab in the control pannel and selecting the NoSounds scheme, disable also "play windows startup sound". Assumption some sound file is corrupted, and locks up still playing 0s and 1s it doesn't quite understand.
Check the Mixer, to be sure the programs are not being cut off that way, while IN there or in the playback/speakers areas , see if the visual levels ever show or not when a sound is supposed to be played, which indicates that the software is playing the data the hardware not getting it correct.
do the definitive full reset of the stored mixer data (in registry) which is show in this answer https://superuser.com/a/991693/98855
Nuke things in the task manager. If something has locked up a resouces on your computer, a quick live way to do discovery may be to just start taking programs out with a process tree Task End. Sort by items running as your local user (user name) right click and select "End Process tree". Nuke meaning to kill them, diabolical but possible. Save anything your working on first.
Discovery in the Resource monitor: Why is that program working the disk and doing I/O over the network? Any program activly still playing sounds, will probably show up as churning the disk, or sucking down data off the network. In the windows resource monitor select the Disk tab, and check out the Disk Activity section, for programs presentally reading data. In the Network tab, do the same thing. Both of these views have a long decay time, giving you plenty of time to see a programs activity, and to/from where.
Get the program AutoRuns (from the source), which is a systernals program that will allow you to store what you have there, then disable vast majorities of things on a windows system. Concentrate first on the "logon" section where programs run out of startup, run , runonce etc. Disable disable disable (reboot required). Assumption there is some fine piece of software running that is trying to play sounds, or unexpectedly locking up the sound driver. There are claims of both malware/addware and viruses that will play advertisements and other oddities. Have a system backup or be very carefull wat you disable as a few thing out of the hundreds will stop proper booting.
Another (probably better option) would be to test first if it happens when booted in safe modes, where most of that stuff would not be run, then proceed to discover what program would cause it by selective disabling.
Along the same lines, a person could begin in "program and features" section of the control pannel and remove stuff they really do not ever use, dont know what it is, or why it is even there, to start the process of stopping un-needed junk by complete uninstall of programs.
Do not depend on MS updates , to provide the best driver for your audio device. while updates may get a certified driver that works , there is no guarentee that it will always be the best driver for your device. Go (direct) to the source of the board makers (motherboard or sound card) and see what drivers they have available, and possibly read about any fixes they have done. Sometimes the drivers at MSupdates have more or less bugs and problems, sometimes the manufactures drivers have more or less problems, there is no way to know which problems you get with either :-), you just use the best one you can for your purposes.
Prefer to fully uninstall, prior to install, and prefer to not depend on "system restore" to return all things exactally right all the time. System restore is more like an emergency return , it certannly is not a full system backup.
Redirected outputs. Back in the control pannel sounds playback, I (myself) find it very convienient to disable all output devices that I am not presently using, also including the recording section. I do not know if it has ever helped, but I do know it limits the possibilities of where a sound is ever sent, no mater how it is (senced) pluged in, or how some software would like to arrange it.
Now that we are down to less items , check out all the properties for the intended output item.
In Control pannel Sounds, speaker section , double click on the speaker (or output) item your using.
General tab- check out how this "jack information" has been configured by your audio chip, todays technology uses sencing to detect what is plugged and not, making it slightly more falable than manually configuring. Something playing but not to the output your plugged into.
Levels Tab- When the sounds stop is anything shown being muted or turned down in this section?
Enhancements tab- while most of these items will screw with or screw up your sound, it would be rarer for them to disable sounds completely, but not impossible. Safer would be to "disable all sound effects" until you know for sure.
Advanced Tab - Really high bitrate output sampling and rates can be selected here, could be some device up and stops working when a very high rate is selected. Set for 16bit 44.1 or 16bit 48.0 types and see how long things work correct that way. Blame the driver and hardware if this changes anything.
If you use Skype, research problems that people have had with that, could be it needs a few tweaks to behave on your system. I do not use it myself, and feel that autoruns disable of startup programs and non-ms services should discover this first (in autoruns section). People have had problems with it before.
If you use a autorunning sounds playing program, or even have Gadget items that use or play sound. Same thing applies, I have not had problems with these items, but Disabling them and thier services from starting (autoruns) should discover the problem quickly. Any Internet connection sound players , which may be playing, but have lost connection, and buffer fill.
Browser playback of flash or html5 (style) could be locking out the audio resources. Even IE browser, does not always close correct. Leftover parts and pieces of a program , still thinking they are playing. Check the task manager (task manager section) and end process tree, any leftovers of programs that did not close properly and completly. Would NOT be effecting things post a re-boot.
Wait till someone comes along with a better answer, or I think up the other things that should be on this list.
