random object spawn in random spawner

so, i got 5 boxes as spawners for spawn 5 sound (just say A-E box). i want to make the first random to randomize the boxes. when which box was chosen, randomize again for another boxes till 4 times but the result before doesnt keep in the array. example, on first random the result was A so the second random have B-E for getting next random. i got the logic but still cant finish the code. need help. sorry for my bad english.

thanks for ur help