X3 BSOD

The looping audio upon crash is the last bit of audio that was in the buffer (looping).
 
BSOD is usually indicative of a hardware or driver issue.
In a modern machine, the most likely culprit to fail is a stick of DDR3.
Thus, I'd test your RAM to be sure all is ok.
I'd follow that up by running a stress-test to make sure the core hardware (CPU, motherboard, RAM) are ok.
If the machine passes those tests without a problem, you can rule out the machine itself.
 
Since the issue doesn't happen when tracking (not using much RAM), I have a suspicion that you may be "RAM starving" Sonar when mixing.  With a full mix (especially if you're using any virtual instruments), it's really easy to blow thru 4GB of RAM (which is the limit for any 32Bit application).
 
As a test:
Install the 64Bit version of Sonar (if not already installed).
Open your project in the 32Bit version of Sonar, use the 32Bit plugins mentioned above), then freeze the results and save under a different file name.
Now, open this new file using the 64Bit version of Sonar.
If you can do this and continue without BSOD, you've found the culprit (RAM starved application).
If that's the case, using a 64Bit DAW application is the only solution.

fooman
Thank you!!! How do you stress test a machine, other than doing the 64bit test you described later in the reply?

You can use Prime95 to stress-test your core hardware.
It puts the CPU under 100% load (sustained).
Note, keep on eye on CPU temps if you run Prime95.

Silicon Audio
If you are getting a BSOD error, you need to tell us the stop code.  That will give us a much better idea of what's going on.  Have a look for "Nirsoft BlueScreenView" on Google.  Make sure to grab the 64-bit version.  It will give you more information about the crash and what caused it.
 
As Jim has already said, applications can't cause blue-screens.  It is caused by bad hardware or something happening in Kernel mode (bad drivers).

 
+1.
 
I had an issue like this yesterday, from here I was able to locate the issue was related to mcupdate.dll. From that I gathered that Windows Media centre was trying to update itself and somehow causing the crash. As I don't use Media Centre on my DAW I uninstalled it.... Fingers crossed no more issues.
 
Your issue will be driver related or hardware related. You might want to post the BlueScreenView report here if you can't work it out. Generally the suspect exe/dll's/.sys are at the top of the list. Still often requires some hunches/guesswork though. The windows event viewer often helps as well...

Had the same issue.  Pulled the CPU, fan and heat-sink out of my ASUS CM1630 case and found a lot of crud on the heat-sink.  Managed to bend some pins on the CPU when attempting to re-insert it. Consequently I ended up buying a new ASUS M11 series.  I've had no recurrence of BSOD.    After seeing the buildup of dust and grime on the original CPU's heat-sink,  I can't help but believe that it was overheating and causing the BSOD.  My rather uninformed guess is that Sonar may overburden the CPU when it is cranking out its stuff. If enough heat energy is not dissipated because of a dirty heat-sink the conditions are then possibly ripe for a BSOD attack.  I had similar problems with another computer a few years back  that was unrelated to Sonar.  Cleaning the guts and the heat-sink fixed it!
 
I'll remain curious as to what you find is at the root of your BSOD atacks.
 

Well if you haven't updated your drivers for a while that's a red flag. Please run windows update several times as well..

Release notes are just guidelines. Often stuff is left out there is a 99% chance there will be at least one undocumented bugfix. I would install you can always roll back. Also please check the optional windows updates which probably won't be installed. Cheers.

+1 Although bluescreenview gives an idea of what may be happening often doesn't find the smoking gun... And the windows event viewer you need to check.

I had to replace the thermal paste in my DAW about a year ago due to overheating, because it actually was reduced to crud.