Boum

" The echo in a Marabar cave...is entirely devoid of distinction. Whatever is said, the same monotonous noise replies, and quivers up and down the walls until it is absorbed into the roof. ‘Boum’ is the sound as far as the human alphabet can express it, or ‘bou-oum,’ or ‘ou-boum,’ -utterly dull. Hope, politeness, the blowing of a nose, the squeak of a boot, all produce ‘boum.
A crowd gathers with Mrs. Moore in the cave, and in the darkness, their cheerful voices produce a deafening and meaningless ‘boum.’ “The crush and the smells she could forget, but the echo began in some indescribable way to undermine her hold on life. Coming at a moment when she chanced to be fatigued, it had managed to murmur, ‘Pathos, piety, courage-they exist, but are identical, and so is filth. Everything exists, nothing has value."
-- from FORSTER, E.M. A passage to India.