Midi playback noise issue

Hey everyone,

Using Cubase Elements 8 + UR22mkII (USB power source), midi instruments (tried with Groove Agent, Prologue and Halion Sonic) seem to produce a hissing, “white noise” kind of sound when playing a note. Especiall noticable with low notes. The sound runs up as I hit a key and disappears as the note fades out. Any ideas what this could be?

Thanks a lot!