Just a disclaimer: Most of this is based on observation and assumptions from experience and should be taken with a grain of salt.
From what I've seen with this glitch, the audio being played is actually just a very stretched out version of the chimes that play over the second logo which you see when a disc is loaded, rather than a separate sample.
Judging by how the console behaves when the glitch happens, it seems that it is constantly attempting to read the disc for something it recognises, but never seems to be able to exit this state. While reading the disc it appears to slow down drastically, as all footage I've seen of these glitches show the logo very slowly fading in over the course of a few minutes.
The audio of the two logos on the system are seemingly MIDI or MIDI-like sequences, as corrupted BIOS data can cause them to play differently or be missing one of the instruments.
Have you ever noticed that when a program playing non-MIDI audio crashes, the sound typically continues until it's over, whereas when MIDI audio crashes it simply loops the last sound it played? This seems to be the case with the glitch's audio - it gets stuck playing the first note of the chimes in a loop, but since it's simply running very slowly and not a crash, the system finally makes progress (when the logo fades in another step) and manages to move onto looping the next note. It then repeats this process until the original sound is finally over.
As for the graphics, I highly doubt that it's anything intentional. Since the PS logo is a polygonal model and not pre-rendered, a corrupt BIOS can hide or displace some of the polygons. Since different footage of the glitch shows the logo glitched in many different ways, it's fairly safe to say it's unintentional and that the glitchy graphics are just that - a glitch.
