I.
noun
ADJECTIVE
▪ faint , gentle , soft
▪ low
▪ high-pitched
▪ constant , steady
▪
I could hear the constant ~ of distant traffic.
▪ background
VERB + HUM
▪ hear
PREPOSITION
▪ ~ of
▪
the background ~ of the air-conditioning
II.
verb
ADVERB
▪ quietly , softly
▪ loudly
▪ happily
▪ tunelessly
▪ along
▪
I was humming along with the music.
VERB + HUM
▪ begin to
▪
He began to ~, somewhat tunelessly.
PHRASES
▪ ~ to yourself
▪
She was humming softly to herself.
Hum is used with these nouns as the subject: ↑ bee , ↑ economy , ↑ engine , ↑ machine , ↑ refrigerator
Hum is used with these nouns as the object: ↑ bar , ↑ melody , ↑ snatch , ↑ tune