OK, so this was quite similar to Moving Pictures - but this was about "Music with Rocks in". With the added angle of Death, becoming a bit depressed and disappearing, meaning that his grand-daughter Susan has to take over.
It's about Buddy (plays a rather special guitar - looks abit elvish), Glod (plays the horn and likes to decorate hotel rooms) and Cliff (plays the stones and can knock out his own teeth). The music they play has a beat and you can dance to it, its alive.
Also features the librarian, wizards in leather jackets and the Death of Rats (SNH SNH SNH)
It was good fun, not one of the best Discworld books, but did have some nice lines in it ("We're on a mission from Glod", being my favourite).