It's beyond 'loud noise', it's specifcally an issue with the reservoir and pump combination. With two working in serial, one of the major issues is that the inlet to the res is directly next to where the pumps draw water. When both pumps are maxed, the water from the inlet displaces the water in the res in a wave pattern as if you did not fill the res the whole way. I think this is the source of the issue with the major pump noise.
In addition to that, the pumps when secured tight enough to not leak actually rub against the reservoir making a grinding noise. When you loosen the pumps enough to stop this, you get really really close to leak territory.
I can't imagine that both of these design flaws would have made it out of Alphacool's testing, but I'm seeing a few people with the exact issues.
Also, I went to straight power as well as powered through my 30W fan controller. The fan controller was able to run them at a higher speed than straight power, which is really odd. The noise was consistent throughout the range of speeds.