All IOS system will definelty cause some irrating noise,on the return side.unlike sump, the full system are more fully enclosed and housed all the Essiential equipment(especially,the skimmer) within a cabinet which can indeed contain the noise level and much more neater.
I see most of my friends which had done a good quality top enclosure in order to shield off some noise and disperse lux level of the light to their bedroom during the nite.