Noel,
 
I am not at the DAW for the next six hours but I will address your suggested tests before the night is out.
 
The project only opened twice today when I got the noise with no crash. After that I was unable to open project without excluding all UAD plugs (1176 newer version, LA-2A, Helios maybe one more). And then, I could not reproduce the noise.
 
Specs:
SONAR X64, WIN 7 64bit, UAD Ver 5 or 6 (I cannot recall which) on two UAD Quad cards.

hate to ask a dumb question, but what is UAD

redbarchetta
hate to ask a dumb question, but what is UAD

http://www.uaudio.com/

This is not what I wanted to here ....

StarTekh
This is not what I wanted to here ....

Slow down, remember I'm at least one rev behind on the UAD plugs (maybe even 2). We'll know in about 5 hours if the problem is related to that scenario.

Good news,
 
After updating to version 7 of UAD the problems went away. No bug here.... move along.

Bad News. 
 
Since I did not upgrade the UAD LA-2A to the LA-2A series when I open this project I am now informed (after updating to 7.1) that the LA-2A is not installed. So far so good. 
 
But..... when I try to delete it from the track SONAR crashes.
 
So now I'm begining to think the original problem was tied to the existance of the (original) LA-2A in the project. 
 
I submitted the mini dump and got assigned CWBRN-19986. 

For anyone wanting to try and confirm here is a link to the project that fails.
 
Of course you need to skip the search for audio files but once loaded, try and delete the non existant LA-2A from the bass track. That is what cause the crash for me.
 
https://dl.dropboxusercontent.com/u/1227448/The%20CHB%20Song.cwp

Can't you delete it from your X2a installation, save it & open it up in X3?

Ed, I'm getting this problem, too.  I opened a project from X2 in X3, and merely added 3 instances of the the new PC tape emulator to the project.  The only other plug in in the song is Guitar Rig 4 LE.  All other plugs are native Sonar plugs.  After the project is open for a while it just starts motorboating while at rest.  This has never happened to me in any version of Sonar going all the way back to the beginning of Sonar.  I'll be watching for a solution.