I don't know if this will help or not, but I had a similar 'lock-up' problem early on with my Pa600, but without the high pitch sound ... My dealer got in touch with KORG and they let me swap for a new one but the same thing happened ... after a few back and forth e-mails with KORG customer service, it was suggested that I get a new USB drive, format it on the KORG and then use it only for KORG files (song specific styles and STS that I had set up) and midi files loaded from a pc onto the USB drive ... fortunately, no problems since ...
I found KORG customer service to be very responsive and helpful at that time ...