In Sonar 8.5 Producer, you can right-click on the timeline, expand the "loop>" submenu and choose "select loop region." I know this is an old thread but since it's the only place I could find this question when I was searching, I thought I'd post my findings for the benefit of future Googlers. I had the same intent, looping audio at zero point to eliminate clicks. When you use the loop feature to audition the selection and make sure there is no click at the seam, you have to make sure the exported region has the exact same bounds or there will likely be a new click in the export.