No direct DA60 experience here, but alot of other experience, so I must ask have you double checked your prop balance?, or tried another prop?... What size/brand/etc prop are you running? The prop is the first thing that comes to mind... or even the spinner, just make sure everything is balanced, and the engine is mounted securely and tight as it should be. Just things to double check. From what I know, those smaller twins should be pretty smooth runners.. but you do have something a bit off it sounds like.