You may be experiencing a MIDI feedback loop.
A few symptoms of a MIDI feedback loop:
If you are having these symptoms with your Hauptwerk II rig you may want to disconnect the MIDI OUT from the computer from the MIDI IN of the keyboards.
Keeping this connection can sometimes cause a MIDI feedback loop within Hauptwerk if the MIDI outputs within Hauptwerk are enabled.
After the keyboards are configured, you will rarely need the connection from the computer-out to the keyboard-in. If you do wish to keep them connected, just be aware that if any problems arise you should try to disconnect the computer out first to see if that is the problem.