This is a great example of something you’re probably already doing. Richard Mayer and others have discovered that when graphics or words are used alone to convey information they are less effective than when used together. He calls this the Contiguity Principle.
But watch out! Other studies show that using an audio track to read exactly what is on the screen reduces comprehension and retention by 79%. The redundancy may signal to the brain that what is being conveyed is less important because it is commonplace. These studies also put the old learning styles in further disrepute. If it were true that appealing to each learning style in your learning design helps people learn, using the audio track to appeal to “auditory learners” should have boosted retention and comprehension, not diluted it.
See Eradicating the Learning Styles Myth for more information.