"Wait", he said slowly. (An actual sentence, from The DaVinci Code).

Issue

Verbal Redundancy

If you treat the adverb slowly like a stage direction, you will say Wait' slowly. Do you have to tell the reader twice?

This is one of those places where visual meets audio. If you didn't write “he said slowly”, how would you convey that to the reader? But since you are now talking out loud, you don't need to tell the listener again. Your nemesis is the current definition of an unabridged audiobook. If you leave something out, technically it's no longer unabridged (though it is long stretch to say it is abridged either). You can make up your own mind whether you are going to include every said slowly, shouted and whispered, or not.

Similar issues

"Help!" he shouted. "I'm under the bed", she whispered.

• Shouts and whispers: Don't really shout or whisper. A microphone is very sensitive, both to volume and to lack of volume. If you shout, because it says “he shouted”, or you whisper, because it says “he whispered”, chances are the results won't be what you want for an audiobook. Recording equipment is generally set for picking up a normal speaking volume. Sudden loudness can result in a distorted sound. If you are too quiet, you won't be able to distinguish your words when you play it back. Use a dynamic volume range, but do not vary too far from the middle.
• Keep the attribution neutral: Don't let the attribution carry the same tone as the spoken portion. For example, you are reading this sentence: "Shh, come here and keep your head down," he whispered., don't whisper the word whispered. Likewise, if the line is "Run, Jack!", she shouted., don't shout the word shouted.
• Timing: Think back on what you intended, and try to say it that way. If the sentences are. 'John laughed. “Who did you think it was?”', where is the laugh? Is it before he says “Who, or is it describing how he is saying “Who …”? If it's before, did you intend the tone to carry through the “Who …” or to be a separate action?
• Attributions at the end: Make a note if you put an attribution at the end of a character's spoken words. The 'he said sarcastically' or 'He said jokingly' should apply to the whole speech. If you do muff it, do a re-take.