So now I received another unit (8 numbers difference with the previous serial number). It has the same issue, which makes me wonder if there is something I am not getting, or it’s an issue related to the same set of chips. I initialized a sound and played with it, but the issue is exactly the same. Technical support says “statistically” is very unlikely that two boards have the same issue, and that it might be related to my headphones (the only gear I have in the US to try the keyboard). They also say that they feel pretty certain the issue is related to the headphones, which I frankly don’t get how it could be. It’s always the same two notes (4th and 5th), and cannot figure out how it would be related to headphones. I will buy new headphones tomorrow and try them, but at this point I do not feel sure to go back to my country with any of these. Any suggestions are welcome, and thanks again!