Yesterday I experienced two radically opposed versions of being in tune: The first, by far the more moving, was five live voices singing a mass by the Spanish Renaissance composer Tomas Victoria. Lustrous. Glorious.
The second occurred much later in the day, this time a radio broadcast of a singer/songwriter/cellist recorded on multiple tracks playing various cello lines and singing. Cooooldud..... if you get the drift.
Ironic that the same singers who had produced the Victoria went on to improvise!! in their several voices the singing of a Gregorian chant. It was marvelously random, based on a kind of tuning that I use all the time with my students. Learning not just to tolerate but to enjoy random sound is a mark of true musicianship, in my view.
All sound, however consonant, contains elements of random. Paying attention to them can be frightening or liberating, depending.