hum

The visit made the papers. Audiences rewarded the orchestra with robust ovations.

It was the kind of reception not always given the Philharmonic at home, where it has to compete with the loud hum of major international orchestras regularly passing through New York.

hum Show phonetics
verb -mm-
1 [I] to make a continuous low sound:
The computers were humming in the background.
What's that strange humming sound?

2 [I or T] to sing without opening your mouth:
She hummed to herself as she walked to school.
I've forgotten how that tune goes - could you hum it for me?

3 [I] INFORMAL to be busy and full of activity, excitement, sounds or voices:
The pub was really humming last night.

hum Show phonetics
noun [C usually singular]
Our house is on a main road, so we can hear the constant hum (= continuous low noise) of traffic.
There's an annoying hum on this computer.

(from Cambridge Advanced Learner's Dictionary)