In X2 whenever I'm doing a lot of slip stretch editing and playing of audio clips I eventually get a major dropout where the MOTU Audio Express produces a mind blowing scratch-n-screem session. I have to close Sonar to stop it.
 
I use ASIO mode and only get this when editing clips.
 
It seems to be Sonar's fault or the USB connection because I can play other audio devices through it just fine.

So to check... Do you have?
 
Latest MOTU drivers and firmware:
http://www.motu.com/download/
 
Latest motherboard firmware
 
....and latest chipset drivers (if an intel motherboard please check Intel's auto update site):
http://www.intel.com/p/en_US/support/detect
 
Have you run windows update several times and install most of the optional updates?
 
Defragged?
 
Thanks
 
Alex