The “morning stars” in Job 38:7 are the stars in the sky.  The “sons of God” mentioned in that verse are the angels.  The stars and angels joined in praise when the earth was created.

How can stars sing?  During the Triumphal entry into Jerusalem, when the Pharisees wanted Jesus to silence the disciples who were praising Him, Jesus replied: “…I tell you that, if these should hold their peace, the stones would immediately cry out” – Luke 19:40.   In Isaiah 6:1-4 we read: “In the year that king Uzziah died I saw also the Lord sitting upon a throne, high and lifted up, and his train filled the temple.  Above it stood the seraphims: each one had six wings; with twain he covered his face, and with twain he covered his feet, and with twain he did fly.  And one cried unto another, and said, Holy, holy, holy, is the Lord of hosts: the whole earth is full of his glory.  And the posts of the door moved at the voice of him that cried, and the house was filled with smoke.” – even the inanimate doorposts shook in the presence of Almighty God.