I guess noise varies a lot depending on what pump/res you have and what mounting too probably.
I personally can't hear my DDC4.2 unless i really push it very hard when chasing bubbles.
In normal use, can't hear it (always around ~60% +-5)
It costs a bit, but the best solution is always to test for yourself.
I used to consider DDCs too noisy because everyone said so, but in my rig the D5 is waaaay louder. So it may be worth a try, maybe
That Swiftech has some funky impeller, very remisniscent of a beefed up AIO, and from the test i've seen, doesn't behave too differently from a DDC. Worth a shot