Just a quick thought from New Zealand
Make sure the MODULATYION wheel is in the OFF positian
The modulation wheel is next to the Pitch bend wheel
Both control wheels are on the bottom left of keybaard
If the Modulation wheel is partly on it has been known to upset the crystel clear Piano sounds.
I have discovered the modulation wheel partly ON when a music teacher was complaining of extra unwanted sounds when playing as a piano.
The pitch bend wheel springs back to the OFF positian BUT the Modulation wheel does not----silly design ----
All the best from accross the ditch cousins.
Dave L.