When, EXACTLY, does this loud sound occur, all the time, only when you load it, etc? Is it reproducible or intermittent? Are you using any of the new routing features, pre/post or wet/dry? Also, does it matter what type of preset you are coming from (e.g. TremoloVerb to Shimmer creates the loud noise, but Chorus to Shimmer doesn't)?
You might want to back up presets, and initialize the unit as first resort to see if that clears up the problem.