Well, consider that autistic people experience heightened response to stimulation compared to neurotypical people, and it might become clear why some autistic people would take more pleasure from it than most neurotypical people. Overstimulation goes both ways - not only is it painful when the stimulation is unpleasant, but it's also unusually pleasurable when the stimulation is good.
I take great enjoyment in certain sensory experiences which NT people would consider odd, like certain smells, touch-textures, and most of all music. I enjoy a number of different kinds of music and it has an enormous effect on my mood, meaning that I can use it to cheer myself if I feel down. I particularly I love classical music, and certain classical pieces can literally send me into raptures.
As a few others have said, I too consider listening to music a complete task in itself. I like to close my eyes and listen to block out everything else. If music is played in the background, I either tune it out, or am distracted by it, so I'm also quite bemused by people who use it as background noise.