Can you please provide some additional information?
1. Are these projects from prior releases, and if so, which prior releases?
2. What is the makeup of these projects? Midi? Audio? Mix?
3. What are your interface sample rate and Sonar sample rate set to?
4. What is the ASIO buffer size set to in your interface?
5. What audio driver mode are you using in Sonar? WDM or ASIO?
6. Does this occur when you start a new project? If not sure, then please create a new project with the Normal project template, insert an audio track, bring that track into focus, import an audio file - such as an MP3 tune, to that audio track, then hit play and post back as to whether or not that plays back with sound and no glitches.
7. What Windows 7 64-bit flavor are you using? (Home Premium, Professional, Ultimate, Starter), and what service pack are you running on whatever Windows version you are using.
8. Do you have any other applications running that use audio, at the same time you are opening projects in Sonar, and do you have the box checked in preferences in Sonar to allow Sonar to share the audio processing with other applications?
9. Outside of Sonar, does Windows Media Player play back tunes running through your audio interface? Do they sound OK?
10. Was your installation of Windows 7 a clean install, or either an upgrade or re-install?
11. What version of audio interface drivers are you running?
12. Do you have an antivirus program running during Sonar audio sessions?
Sorry for all the questions, I am just trying to get a larger sense of your system, to help me to assist you.
Bob Bone