Melodyne Plugin Problem

[JohnReaper]

I have the latest versions of Melodyne Studio, Reaper and Windows, all updated. When I use Melodyne as a plugin on a track it introduces low level but annoying crackles in various almost random parts of a song. If I use Melodyne as an external editor from Reaper, no problems at all. The crackles from the plugin persist if the track is rendered, so it's not a process limitation. Anyone have thoughts as to why this might be? Thanks