My batch 2 unit was definitely noisier than my batch 1. It seems to me like my batch 1 unit was dissipating a lot more heat through the bottom aluminum plate of the case, thus requiring less work from the fans. The bottom of the batch 2 case was a little warm whereas the batch 1 case was almost too hot to touch.

The batch 2 heat sink is of a different design and has small ridges on the surface that mates with the case. This reduces thermal dissipation through the bottom of the case.

I made my batch 2 unit a little quieter by applying Arctic Ceramique 2 between the heat sinks and the case. I needed 3 x 2.5g tubes - one per hasher.

Edit: I used Ceramque because it is non-conductive. It is easy to make a mess while screwing the heat sinks back to the case because the holes are not easy to align.