As I see it, you have one choice: burn the demonized Metronome.
Apparently, immaterial demons can be foiled by flame, and you will hear screaming as it either causes them pain, or they got really attached to the object in question. Bewarned, if they've protected the metronome with fire retardant from the spirit world, if might not burn. Or it will...but just take a little more time. This might be especially the case if the object is flame resistant in the first place, but regardless, the object won't burn well because of being possessed.
Saying name Jehovah might facilitate the burning, but will cause the demons to scream even more--even though that rendering was mistakenly conjured by medieval scribes a few centuries ago. The demons will tell you NOT to say the name Jehovah...and somehow these superhuman entities who are smarter, more powerful, and have lived longer than us have never heard of reverse psychology.