Edit: and here is maybe the video you were remembering: a video from June 2011 of someone hooking a speaker to listen to the flickering led: https://youtu.be/753-lkao8l0?si=-WqRRuBH644oKTXG But they don't realize this may be an audio chip as the tune isn't really nice or recognizable.
And here is someone who recorded audio samples (no idea of the year): https://www.instructables.com/How-to-Listen-to-Light/
Edit: and here is maybe the video you were remembering: a video from June 2011 of someone hooking a speaker to listen to the flickering led: https://youtu.be/753-lkao8l0?si=-WqRRuBH644oKTXG But they don't realize this may be an audio chip as the tune isn't really nice or recognizable.