That 'shing' sound is probably the sound that happens when a piece of equipment fully spiritbonds - once this happens that piece of equipment can be converted into materia by using the the relevant command (found under Actions and Traits).

As for Commendations, this is a system where players can reward a member of their party who they felt worked well or was just a nice person - only those who are not on your Friend List can be given a Commendation though. There are Achievements you can unlock by getting lots of Commendations so it's worth it (especially as the higher ones give nice rewards, like the gilded magitek armour and parade chocobo).