It might be a temporary issue. It could be caused by simply not being deep enough in the dream. Trying to engage in the dream or simply wait it out may be one solution. Also, be mindful of your own expectations as they will also influence how you perceive in your dreams.

Finally, you may try to exercise your auditory skills during the day to strenghten them. For example, set 10 mins aside where you simply pay attention to sounds in your environment. Another variation would be to focus on the sounds/speech patterns when interacting with people or watching TV. Simply by doing this, you will feel how the entire experience is different and your perception is enriched.

Another exercise would be to play a sound (you can pick anything on youtube) and then pause and imagine you are hearing the sound echo in your head. If you practice this frequently, you will be able to introduce sounds to your dreams even if there are none.