The pump is really what makes the AIOs loud and the H115i and the H100i will have the same pump. 140mm fans will be quieter than a 120mm fan because they can spin slower while moving the same amount of air. But sound is not linear, so if you have a pump that is 30db and fans that are 25db, you don't get 55db when they are together. I would probably be closer to 33db. So you really have to look at the loudest component (which is the pump) and everything else is secondary.
I have a H115i on my gaming rig and it is not too loud, but it really depends on the case though. If you have a quality case, it will dampen the noise. But if you have a cheaper case, then it will be louder. Swapping out the fans that come with the H115i will help some, but still the pump is the loudest part.
You could also go with a air cooler. The Noctua NH-15 is one of the best air coolers in the world and it will do just as good as the AIOs while being quieter. But they are big and don't fit in every case and they don't look as nice (in my opinion). The Cryorig H5 is a good air cooler for $50 that will be quieter than an AIO.