Why are the scene transitions starting to get bad on my SNES?

I started noticing this with super mario world. When I select a new world or go through a warp, instead of the nice smooth transitions I used to get between scenes (like the a swipe or a fade out to black and fade back in with the star pattern) I now see the screen almost jump between scenes. It does this for other games as well. I'm not sure why and I hope it's not my mother board.!