lv455
* If I export audio during this condition, the exported mp3 will be silent except for some clicks.

This kind of rules out hardware/driver issues as the interface does not get involved in offline rendering  - unless possibly you're disabling Fast Bounce...? I assume not because MP3 encoding does not play nice with real-time audio export.
 
My first guess would be that some plugin or Audiosnap stretching is not playing nice with the 64-bit Double Precision Engine. I suggest you disable that for a while and see if the problem still occurs.

So it's still happening? Do you have any "HD Audio" drivers enabled in the device manager? That belong to your video card HDMI output perhaps? Try disabling those completely. 

Sorry, I was a bit unclear in the posts above. No, since I disabled CPU energy saving features, I haven´t had a single hiccup. However, I have only done basic testing and sometimes I might have several days without any issues.
 
Edit: Good point, I actually had some "HD Audio" belonging to the GPU but I disabled them during my last trouble shooting session.
 
 

Sanderxpander
So it's still happening? Do you have any "HD Audio" drivers enabled in the device manager? That belong to your video card HDMI output perhaps? Try disabling those completely. 

After a few happy days of no clicking problems whatsoever, I made some progress on the current project and made a mp3 export. Right after the export, there was a loud "click" and along with it returned this very annoying problem.
 
After some further testing, here are some more observations:
* The problem is most likely to occur right after an audio export (mp3 or wav does not make a difference)
* 64 bit engine on / off does not make a difference*
 
I guess I´ll check at the RME forum as well but it seems more like a Sonar issue, however in that case I would expect to find more about it here on the Sonar forum.

I see you have a Babyface as well and since you´re the only one aware of with this issue except for my self, my theories about this being a Babyface issue suddenly got a little stronger. However, I don´t understand why this would affect audio exports.
 
Yes, latest version of Sonar (and Babyface drivers as well).
 

sharke
I used to see this but not any more. Are you running the latest version of Sonar? Because there were a couple of plugins which caused this issue which have since been updated. I think it was the concrete limiter and channel tools. In fact channel tools used to do this to me all the time. 

I have a Babyface  which I use on my laptop, Top class no problems.

I am not sure what is causing your problems, you have gotten really good advice here too.  I do not normally export to mp3 but use flac and sometimes wav and have processed some large files and never had my Babyface act up in that scenario, or any situation for that matter.
It is possible you have a defective unit.
BTW:
I swear by RME having used their gear for over 5 years without issue, I now own three RME audio interfaces:
I have an RME HDSP 9632 at home with Sonar Platinum and Win 7 Pro on an i7 desktop with 18Gb of ram.
On the road I use a Babyface with my Laptop, a decent Lenovo with an Intel i5 and 8G of ram running Windows 7 Pro and Sonar X3e. Never had a problem with the BF on the road <close to a year of road time by now>.
This last trip I forgot my BF so I picked up the Babyface Pro.
Wow! what a difference, the Pro is incredible, it just seems to have more 'guts' is even cleaner, if that is possible and seems to have more headroom. Now that I am back home I want to try the BF Pro on my home machine in place of the HDSP 9632. Perhaps I will keep using the BF Pro at home too!
 
Check with RME and let us know how you make out. Cheers, Dave
 

Ok, time for an update!
 
First, I tried with another USB connected soundcard (Cheap 2$ Aliexpress thing): exactly the same issue, regardless of driver mode. So I guess this rules out the Babyface.
 
Second, I tried to improve my "Google Fu" while looking for more information on the subject and I did find some other threads describing the same phenomena here on the forum:
http://forum.cakewalk.com/Channel-Tools-POP-then-no-sound-m3345888.aspx
http://forum.cakewalk.com/Loud-Pop-from-distortion-plugin-when-I-save-meter-stuck-at-9db-m3201094.aspx
http://forum.cakewalk.com/Anyone-seen-this-potentially-dangerous-max-output-bug-m3245568.aspx
 
I´m off to do some more "safe loading" / plugin disabling trying to find what is causing the issue.
 

Thanks, I might add that if the Babyface would be broken (I bought it second hand for several years ago), I would probably get the Pro. However, it seems that I´m not getting the Pro right away since my BF is working fine but the Pro seems to be a very nice unit indeed.
 

cw4davo
 
This last trip I forgot my BF so I picked up the Babyface Pro.
Wow! what a difference, the Pro is incredible, it just seems to have more 'guts' is even cleaner, if that is possible and seems to have more headroom. Now that I am back home I want to try the BF Pro on my home machine in place of the HDSP 9632. Perhaps I will keep using the BF Pro at home too!
 
Check with RME and let us know how you make out. Cheers, Dave