A monotonous sound increasing in volume and seeming to descend from above.

Croaking of frogs - the dull, monotonous sound was all that the girl could hear.

The echoing, monotonous plopping sound of dripping water grew louder.

In the long silence there was born upon Bradley's ears a faint, monotonous sound as of running water.

The hoarse, monotonous sound warned of battle to come.

The staring eyes, the monotonous, metallic sound of her voice frightened the squire.

There was a strange, tiny monotonous sound that was almost inaudible.

The lullaby blurred into little more than a monotonous sound.

The monotonous sound of a carefully played piano came from the body of the hall.

Inside the factory, there are the same monotonous sounds associated with any production line.