The Invisible Man vs. The Human Fly

Tômei ningen to hae otoko is a movie starring Ryûji Shinagawa, Yoshirô Kitahara, and Junko Kanô. A ruthless serial killer with a peculiar method of stalking and killing his victims comes face to face with a police officer turned...
A series of ghastly murders are being committed. The one similarity in each of the murders is that a weird buzzing sound is always heard right before the murder occurs. Is the killer invisible or possibly some other incredible creature?