I have the 400i with the DC pump. They dont offer the AC for the 400 series. Ive had it two weeks and must say its whisper quiet and its skimming amazingly. Seriously this Deltec is a beast of a skimmer!
I bought the 1000 AC version because Deltec parts are hard to get. The advantage to the DC version would be easier to tune and noise. The AC version is not loud but I am sure the DC version is quieter.