Cla 250 Mercedes Benz is making a dadada.noise when air is on high volume

I'm so sorry, it's so hard to know what a noise could be via a forum like this. You really need the ears of a trained technician to hear the noise and give advice. Seek guidance near you. As a side note, noise coming from the dash area when the fan is blowing could be coming from debris in the air box that is contacting the fan blades. Sometimes you can access the cabin air filter and see if there is debris in there you can clean out. Just ensure the fan is off and vehicle is off when you do this!