Went on and on ...

• Sounded like a didgeridoo
• Spoke in a monotone
• Used no inflection, maybe
• Buzzed like a bee
• Uttered in a monotone
• Went (on) monotonously
• Talked in a monotone
• Spoke tediously, with "on"

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 ...