Hi Boni,
I am replying on behalf of DELL-Sundeep B. In order to assist you further, I would some more information.
Are you using external speakers or internal speakers?
Since when are you facing this issue?
Did you try to change the audio settings on the computer?
i would suggest you to run the Fixit from the following link http://bit.ly/JvQScV
Please reply if you have any questions.