cat /dev/random > /dev/dsp

Not necessarily the most pleasant sound. [Linux only AFAIK]

For this exercise, /dev/urandom might be better; reading /dev/random will block after the system's entropy pool is exhausted, right?

I'd consider it unlikely most reasonably sane people would actually want to pump random data out their speakers for any significant amount of time.

hmmm... how would I make the sound of bits moving around... would probably end up sounding like rain!