I've been trying to open some older projects(some created with X3, some with platinum) and I'm getting this pop sound at the end of it loading.  I believe the pop is an indicator, not the problem.  The issue is the audio tracks can not be heard.  The meters show activity, but sound.  All midi tracks work properly.
 
I can go into the project folder and play the wav files in Media Player.  I've tried to copy the files into the project, but still no sound.
 
 

Hi. This sounds like an issue with your Audio Interface / sound card, and not SONAR it self. What kind do you have, and which driver mode do you use?
All the best.