All of the files I try to export to WAV (or MP3) under X3 are unusable.  They all have a loud fluttering sound throughout the rendering -- but only in places where sound is present.  The quiet passages have no fluttering.
 
The files play absolutely cleanly when I am playing them in real time, but when I play the exported WAV in Media Player, it is garbage.  I have tried every possible option on the File Export dialog, I think and none of them make a difference.
 
To simplify, I created a new project and dragged a little WAV into it.  There is only one track and no effects at all, but still it gets this fluttering.
 
I don't see how this could be related to my driver settings because the problem only happens when rendering (File Export Audio)
 
Is anybody else having this problem?

Try this:
Go to preferences -> sync and caching
Set synchronisation to "trigger & freewheel".
 

Actually, the problem is in Media Player.  I should have checked that.  Somehow the I got my Media Player settings messed up in the course of installing X3.   I believe I had been running Media Player through my Audiobox output.  I did change the ASIO settings a little, and maybe that hosed Media Player.  For now, I am sending Media Player through the sound card on my computer, and it sounds OK.
 
In other words, the WAVs created by SONAR are OK.  I couldn't play ANY WAV files correctly, even ones I knew for certain were good ones.

may I suggest you modify the title to include **solved**?

Mystic38
may I suggest you modify the title to include **solved**?

Yes, of course.  Done.
 
I am still not quite sure what got me into that position.  At one point X3 live playback was doing some audible clicking, so I changed my ASIO settings to the next more relaxed setting.  That cleared up the clicking.  I don't see why that would have affected Media Player.
 
Anyway, I have changed ASIO back to the "normal" setting and set Media Play back to using my Audiobox and both X3 and Media Player are playing fine now.  I am thinking the original clicking might have been a result of the VST scan running in the background, but I can't say that for sure.

I had this problem in X2 - and found that if I rebooted the PC wav's would play fine. I think it's a media player thing - sometimes, as well, media player would not play CD's immediately after it, itself, had burned them....again, rebooting was the only thing that worked.