thrum 1 
(thrŭm)
(thrŭm)v. thrummed, thrum·ming, thrums
v.tr.
1. Music To play (a stringed instrument) idly or monotonously: thrummed a guitar.
2. To speak, repeat, or recite in a monotonous tone of voice; drone.
v.intr.
1. Music To strum idly on a stringed instrument.
2. To speak in a monotonous tone of voice; drone.
n.
A thrumming sound.
[Imitative.]