Spoke monotonously

• Talked monotonously
• Uttered in a monotone
• Went on and on and ...
• Talked in a monotone
• Sounded like a didgeridoo
• Buzzed like a bee
• Sounded like bagpipes
• Hummed in a dull manner
• Spoke so as to put people to sleep

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Drone \Drone\ (dr[=o]n), v. i. [imp. & p. p. Droned ; p. pr. & vb. n. Droning .] [Cf. (for sense 1) D. dreunen, G. dr["o]hnen, Icel. drynja to roar, drynr a roaring, Sw. dr["o]na to bellow, drone, Dan. dr["o]ne, Goth. drunjus sound, Gr. ? dirge, ? to cry ...