This is very common on new units. When the manufacturer is installing the fresh water tank, they have to drill out the holes for the connections. When they do this, lots of little plastic flakes fall into the tank and they NEVER clean them out. That's usually what causes this problem. The best thing to do on a new unit is to install an inline screen filter BEFORE the pump before the pump is used for the first time. This is also a good idea for the future because it's not uncommon to get occasional particulate in the city water you'll be using to fill the tank.
