Opera Singers can be found in Happy Town standing on top of the pillars, or in groups of five/six on the ground. They are missing their bodies from the waist up, except for their hands, which are wearing white gloves. Observing the opera singers causes a vocal noise to be heard.
The triangle floating above their waists resembles the heads of the ghosts from the Violence District. This suggests that the opera singers are ghosts. Their hand gestures makes them appear that they are singing.
In the Dream Journal, one of the dreams talks about the bottom half of an Italian opera singer (which can be seen here and here). These objects match the description of the singer in the Journal, including the low definition opera singing that can be heard.