Korg Poly800/EX800 Users

Just wondering if anyone has this happen when using the acoutic piano 
patch on their poly 800 mk1:

a.) press down any of the keys on the lower two octaves and you get a 
normal sound

b.) hold down one of the keys in the higher octaves and press the 
same key as in a.) this time you get a much fatter sound which sounds 
kind of staticy