The flute is symbolic of the spine which has apertures. On activation of all the chakras, the vayu blows through this spine in the sukshma sharira and enables the tapasvi to do sattvic karmas and other high class siddhis. Swami Sivananda had written that on reaching closer to the inner divine a tapasvi hears the sound of the flute and bell inside his head. (not like a hallucination).
Peacock feathers have crystals which enhance the powers of the pineal gland which too have similar crystals. The colours of the peacock feather are the same as that of the sun seen in NASA photos, and the surya bija mantra '”Om Hraam Hreem Hraum Sah Suryay Namah” activates shaktis as described in Ram and Krushna Leelas. Peacock is also vahan of Kartikeya who is metaphorical 'son' of Siva, or the divine powers produced by meditation on Siva.