Over and above all, the Lord used to play His celebrated flute. The sound vibrated by His flute would give His friends such transcendental pleasure that they would forget all the talks of the brahmananda which is so praised by the impersonalists. These cowherd boys, as will be explained by Sukadeva Gosvami, were living entities who had accumulated heaps of pious acts and thus were enjoying with the Lord in person and were hearing His transcendental flute. The Brahma-samhita (5.30) confirms the Lord's blowing His transcendental flute.
venum kvanantam aravinda-dalayataksam
govindam adi-purusam tam aham bhajami
Brahmaji said, "I worship Govinda, the primeval Lord, who plays on His transcendental flute. His eyes are like lotus flowers, He is decorated with peacock plumes, and His bodily color resembles a fresh black cloud although His bodily features are more beautiful than millions of cupids." These are the special features of the Lord.
Srimad Bhagavatam Canto Three Chapter Two Verse Twenty Nine