I am running Hauptewerk 4.2.1.003 on a Mac Pro, 6 core, 512 gb SSD, and 16 GB memory. The audio interface is a MOTU 828x connected via thunderbolt. It serves as the MIDI input for the keyboards and as the audio output for 8 channels of audio to the 4000 watt sound system. The MOTU driver is 1.6.68717. We leave it on all the time. Using the stock St. Annes Organ. Converted and old 2 manual keyboard and pedalboard to MIDI using MIDI warehouse boards. That all works fine. We have a main monitor 16 by 9 ration off to the side and three ELO 1215L touch screens at the organ, left jamb, right jamb, and assignable ( general purpose ). AS I mentioned it is left on all the time and a UPS is installed. About every 2 to 3 weeks we have to reboot the mac because the audio fails. The failure occurs in that when pressing any key on the keyboard a low frequency sir pulsing sound occurs ( out organist calls it bat wings ) is all that comes out of the speakers instead of the pressed not. Restating the Mac will always restore it. I do not know if Haupterrk. is losing the ability to generate tones and send them to the MOTU or something else. Sound is being produced by the MOTU ( the bat wing sound ) and all the keyboards and MIDI commands are still coming in so if it is a driver issue with the MOTU is is very selective. Any Ideas?