thrum
     n : a thrumming sound; "he could hear the thrum of a banjo"
     v 1: sound with a monotonous hum [syn: {hum}]
     2: sound the strings of (a string instrument); "strum a guitar"
        [syn: {strum}]
     3: make a rhythmic sound; "Rain drummed against the
        windshield"; "The drums beat all night" [syn: {drum}, {beat}]
     [also: {thrumming}, {thrummed}]
Source: WordNet® 2.0