The fan rpm is quite high.
Yeah at 2800rpm each it will be quite noisy. I know just one running at 2500rpm on a S1 was noisy. But maybe the ambient temp where they test is very high. Who knows.
From the description:
Quiet: The customized heat sinks mounted to the hash boards, one box over S3 to control the air flow, two fans mounted on both front and back ends that mean fans are able to work at lower speed to dissipate all heat easily. This design let S3 run at much lower noise level.