Yes... A real Atari does the same thing! That's what the processor and the other chips produce when the machine is started with no ROM to be executed.
I tried to implement the emulation at the hardware component level as accurately as I could. It happened spontaneously!
Where does the randomness come from though?
When the processor tries to read the game program from the empty cartridge slot, it ends up reading random bytes from the data bus. Its like a random program commanding the video and audio hardware!