Pretty self-explanatory, when a Noteblock is placed on Blue Ice, it plays the sound a Note Block would normally play on grass or dirt instead of normal ice.
Related issues
duplicates
Comments
galaxy_2alex
ampolive
Actually a duplicate of MC-131491.
migrated
Packed Ice is the one that has the harp sound - both regular and blue ice do not have a special sound tied to them. As per MC-91091, this is a feature request.