So, I was getting a little annoyed with my DS1515+ in that the fans were starting to age and creating a lot more noise.
A quick solution was to swap them out for Nocuta NF-A8 FLX fans and to use the rubber fan mounting grommets that come with it to attach the fans to the fan shrouds. These help absorb the fan vibrations and further lower the noise from the new fans.
An additional fix, for HD sled vibrations, was employed to further lower the overall noise from vibrations in the case.
For a tutorial on how to do this case mod see https://www.youtube.com/watch?v=z-aTvVo59tY it works by using the cushioning properties of the loops part of a strip of adhesive Velcro tape.
When the drive sleds are re-inserted into the case they rest on this and it absorbs their vibrations. The result is truly awesome if you were suffering from too much noise from the drives vibrating in their drive bays.
Infonomicon 