The floor was polished smooth, and there was a subtle hum surrounding them.

He could feel a subtle hum in the deck below his feet as the Valiant accelerated to the speed of light.

Without so much as a flash of quantum dissolution or even subtle harmonic hum.

One must also be sure that all equipment is grounded appropriately together, or subtle hums will likely result from the formation of ground loops.

The pan quickly began to crackle amid the subtle hum of undisturbed oil reaching a boil.

The ward room was silent, except for the subtle hum of the station's power generators.

The lift's movement was imperceptible except for a subtle hum.

The banks of instruments sprang to instant life and a subtle, almost imperceptible hum filled the air.

People were starting to make the connection between them and the agent, and a subtle hum rose as they commented among themselves.

His expression changed at once, and at the same time a subtle hum, complex as music, shook the air.