For a "loud sound" or resonance, the piston must be at the position of a node.

Therefore the distance the piston is moved between 2 adjacent resonances is l/2.

(36.4 cm - 5.2 cm) = 3X(l/2)

l = 20.8 cm

v = fl or f = (340 m/s)/0.208 m = 1640 Hz