If you say you made a clean install of win7 i would say to 100% it has to do with a win7 process.
The point why i think is because you have the crackles in a new procet with a high buffer.
Are those dropouts crackles frequently?
Have you checked the asioperformance with latencymon?
With latencymon you would get a detailed information about the dropouts.
Greet Bassbase