Someone keeps following me and whistling and I don't know why

I've been a subject of ridicule for my condition for basically all my life because nobody can understand that sound feels like a cheese grater on my nervous system. But this is a new low. Some one, I do not know who it is, is actively following me and whistling the exact same tune, everywhere. In the supermarket, at the park, at the mall, even when I step out of the yard I hear him. Nobody believes me, and I'm sick of being a damn target. I'm legitimately afraid to leave my house now.