NES Emulator Woes

[triplesycs]

Hello,

I am attempting to play Adventure Island on a NES emulator. However, I keep running into this weird bug/error/something. Some of the characters/enemies in the game flicker. I have attached a .gif to show the problem.

I have tried three different ROMs and MULTIPLE (lots) emulators. When I watch videos of the game on YouTube, the real system does not exhibit these errors.

Please, any help would be appreciated.