Just thought I'd post an update...
I've had this unit replaced, but had the same crackling problem on calibration.
This was after setting up the unit without a PC. Once set up via PC & loading the software however, the unit is fine. So much for the setup without PC! I now need to check tonight whether the Sine / sub test tone works (it didn't before)...

568, 558, Sony 7700 DVD, M&K - S125 L&R, S125C, S85s, SS150THX surrounds, MX350THX subwoofer.