Although it might sound dumb or odd, have you checked the quick release's tightness? Also, are your pedals one piece body or caged? The latter ones can sometimes make "noises". Have not much experience with cassettes, but I had a Shimano cs-hg51-8 that would "clunk" when powering on it; it had a smidget of play corrected with an aluminum shim between the gear cluster and lockring. Good luck!