Temporary malfunction of the Golden Mask 4 Pro WD

After switching the frequency from 8 kHz to 18 kHz something happened... I was not able to set a proper ground balance. It looked like the ground balance function stopped working, combined with a strange metallic sounding tone. I looked if the headphone switch is in the right position, but it didn't cause the issue. Switching the frequency back to 8 kHz was not a solution. At 18 kHz one can hear the different metallic sounding tone very clearly. After turning the machine OFF an ON again, the problem disappeared and all went back to normal. I had no issues since then. I hope this was a one time of...