Is it possibly caused by external clocking? Something to check if you have anything connected via digital connections(like a lightpipe preamp?). If you only need to do this for a current project, Serato Pitch 'n Time Pro does this(arguably) better than any other method and it would render new audio via AudioSuite processing. Serato offers a free 2-week demo if you want to check that out(as the audio is rendered, losing the plugin after 2 weeks is not an issue)
