I know what is wrong, I have had a couple such reports and we found that the wrong air intake was used, the bottom portion of the pump. The DC version needs a different model from the AC version and this was a production mistake. I will have the right intake here next week, if you pm me your address I will send one. The air intake nipple position in relation to the impeller causes a buffeting with the speed of the DC pump. You can run it for now and the new part will solve the noise.
I would just adjust based on what collects in the cup, too dry, turn up the pump speed, too wet, turn it down.