bubble noise

Do Tunze waveboxes necessarily create a "breathing noise" as the box fills and empties? Is there still water/air noise at the lower wave settings? I'm talking about this kind of noise: Thanks a lot!

I have an external skimmer and the feed returns back to my sump. The return water flow has a lot of bubbles and as such it makes quite a bit of noise. I thought of a sponge in the pipe but that would end up and a nutrient trap I think. Any ideas on a solution?