Whistling noises and weird conversation

[Duolingo]

So I was in Sleepy Hollow fighting the Headless Horseman like all people do, but when fell down because of his own grenade I took advantage to kill him with the sword and dagger but when Shay slash down the screen goes black but HUD still present and there is this weird whistling noise that seems whistling some sort of a song and there is a conversation voice between a male and female and the conversation voice is very loud and seems close not like the other conversation you hear while walking down the street, after a whole the conversation stopped and only the whistling noise. Since the HUD is still on my screen I ran as fast as I could to Morrigan by seeing the minimap since the Headless horseman still unto me I cannot fast travel, but when I reach the pier the arrow in the minimap is stopped moving. I was finally able to get out of this bug(?) By replaying mission on progress menu.

[Duolingo]

Actually I just wanted to know what happened

[J_Frosty™ ©]

the headless horse man is in ac4 or ac3... cant remember which but i havent seen anything about the headless horse man in rogue....

[Duolingo]

Originally posted by TheFrost^4JinX» ™:

the headless horse man is in ac4 or ac3... cant remember which but i havent seen anything about the headless horse man in rogue....

Actually there is.. you can go to Sleepy Holow church at night and suddenly a red enemy pointer thing will show up.