Generally,the experts are not always the experts. They may think they understand what goes on, but if they did, we wouldn't have so many people with conflicting views being called experts. Well that 's what I think, but lets look at what the experts think may be the mechanism by which people may have auditory hallucinations. There seem to be two main theories of how hallucinations in general and auditory hallucinations in particular are generated. One group of ideas uses the psychological model and the other uses the biological model.
Lets consider the psychological model first.
One of the explanations for the occurence of auditory hallucinations is linked to the idea of classical conditioning. Usually when he did experiment son his dogs he would muzzle them and harness them to a wall and then feed them some meat powder. The dogs would then slobber all over the place because of the tantalizing food. Well, one day Pavlov, after many occurences of this routine, Pavlov discovered that the dogs started to salivate when he put on their harness even before he fed them the powdered meat. This was interesting because he thought that the dogs salivated because they had the food in their mouth, but here the dogs were salivating without the food.