Hey Daniel, thanks for your reply.
I just tried turning off the Webkit Graphics Acceleration but no luck. Here's a screenshot of the kind of thing I'm seeing. The bottom right should be a seamless little animation but you can see two sides of it with the white outlines. Again, this doesn't seem to appear on every computer I check it on. Weird huh!
Oh, and I'm currently only seeing the issue on a 2012 non retina 13" Macbook Pro, using Safari.