I just built a similar program in Node.js with node-rpio. I had it output random numbers to a 8x8 neopixel grid. To do this I hooked up all the GPIO ports to floating wires, and would loop several times each loop recording 8 pseudo randomly chosen wires into one octal. I would then turn it all into a string like this: "123-5-34,0-67-98,255-89-43, ...

" As you can see, each pixel has a set of 3 numbers to make up RGB. This is then sent over serial to the Arduino which displays the picture. What i found was stunning. These numbers are in fact random, but not from random events. The wires are picking up radio waves! I could clearly see a consistent wave pattern on the pixel grid, and it drove me crazy trying to figure out why. To test the wave interference theory, i simply held up my phone to the wires. As soon as i got within 3cm the program mysteriously crashed with 100% consistency. I then bundled all the wires together with tinfoil. This caused the display to go completely dark, until i moved my hand within a meter. The closer my hand the more visible the wave pattern. It's also worth mentioning i did not connect ground to anything, so no noise was coming from there. Here's the source code: github.com/triforcey/neo-pixel