If the extra note is significantly outside the normal range of the instrument, this sounds as if the extra note is a keyswitch. To let a keyswitch fulfill its purpose and not be audible, one must apply the proper expression map to tell the instrument how to interpret the keyswitch note.
Sometimes the VST/instrument publisher supplies the appropriate expression map, but sometimes they leave that job to the user.
Search here to see if an appropriate expression map exists for your instrument.