Sound effects and multiple narrators in dialogue definitely have their place: in audio drama. In an audio drama, the story is presented in play form. There is dialogue and foley and, all this meets the listeners expectations. Some great examples are The Importance of Being Ernest (by Oscar Wilde; performed by a full cast starring James Marsters,) The Maltese Falcon (by Dashiell Hammett; performed by a full cast starring Michael Madsen) or Don Pendleton’s Mack Bolan series as produced by Graphic Audio.
BUT, in a non-dramatized audiobook, sound effects and dialogue between narrators are distracting. Once absolutely verboten in straight narration, the practice of adding sound effects seems to be creeping in. In Beat the Reaper (by Josh Bazell; narrated by Robert Petkoff,) the narrator’s performance is spoiled by elevator music, the sound of lapping water and, even an echo effect for certain characters’ lines. In The Woods (by Harlan Coben; narrated by Scott Brick) certain lines are enhanced to make them sound like a voice on the other end of a telephone line. Clever, but again, distracting. I worked on a title which involved dialogue between narrators and against my advice, the narrators’ lines were recorded separately and mixed in post. I’m not sure of the effect; but my objection was that the natural give-and-take dynamiic of people in a conversation would be absent.
If the book has multiple points-of-view in it, then multiple narrators are acceptable, though I know of some purists who object to even that! Character delineation is facilitated more effciently by casting multiple narrators for multiple POVs and actually serves the book better.
And, finally, a little note about music: Used sparingly and appropriately at the beginning and the end of an audiobook, it’s great! But when the music goes on too long, undercuts the narrator’s voice, used interstitially between chapters… it’s annoying. Ironically, when I do want the music, it’s cost prohibitive to include it! The rights to even a snippet of music are expensive and yet I can’t help but wish it were in place for audiobooks about music or musicians (i.e. Steven Tyler’s memoir Does the Noise in My Head Bother You? by Steven Tyler and David Dalton; narrated by Jeremy Davidson.)
There are always exceptions, and I’m open to them; just so long as the book is served best.