S2421HN, no sound?

Hi, I recently bought this S2421HN and I'm currently struggling to fix the built-in speakers. I have set them as the default output and when testing them, the green sound line is showing an output but the speakers don't produce sound. However, if I plug in headphones in the back of the monitor, the sound is just fine via the headphones. Could it be that the integrated speakers are faulty themselves?