hum 
/ˈhʌm/ verb
hums; hummed; hum·ming /ˈhʌm/ verb 1 [no obj] : to make a low continuous sound
▪ The garden was humming with bees. ▪ The refrigerator hummed in the background. 2 : to sing the notes of a song while keeping your lips closed [no obj] ▪ I was humming to myself. ▪ We hummed along to the music. [+ obj] ▪ Can you hum the tune for me? = Can you hum me the tune? ▪ I hummed a little song. 3 [no obj] : to be very active or busy
▪ By noon, the office was really humming. ▪ The restaurant hums on weekends.
▪ The garden was humming with bees. ▪ The refrigerator hummed in the background.
▪ By noon, the office was really humming. ▪ The restaurant hums on weekends.
— hum noun [singular]
▪ the hum of insects ▪ We could hear the hum of conversation from the next room.
▪ the hum of insects ▪ We could hear the hum of conversation from the next room.
