Be quiet Dark rock pro 3 not so quiet?

Something doesn't sound right. Maybe the fan speed or fan curve is set really high in the bios. That doesn't explain the poor temps though. It would be unlikely but it's always possible to have a faulty unit regardless what it is. I'd suspect something with the mounting though. I'm using that very same cooler on an i5 4690k oc'd between 4.5ghz and 4.6ghz (summer/winter).

My drp3 has never hit max fan speed under load. I got it to do so once because I was curious about the max speed decibel rating. In order to get it to run full speed I had to shut down every fan in my case. No intakes, no exhaust and I ran p95 v26.6 with the cpu oc'd to 4.6ghz. Then I finally got the fans to ramp up. Under normal conditions with case fans running it basically idles all the time and it's very quiet. My ambient temps aren't the greatest either, it's often 30-32c ambient during summer, right now the room is at 25.5c ambient and it's 6am. The sun isn't even fully up yet. My cores are running between 5-15% load as I type this and the cores are 30-33c.

Double check that when you're getting 50c your cpu is actually idle. If it's at 15-20% use, it's not idle. Even if you're not actively using the pc something else may be running, windows updates, antivirus etc. Try using realtemp to double check, speed fan isn't always that accurate. It might be worth downloading something like hwinfo64 and checking your core voltage as well, make sure it's not running excessively high. For stock I'd imagine the vcore to be somewhere around 1.1 to 1.2v.

One trick I learned when installing the cooler, it helps to install it to the motherboard outside the case. What I actually did was installed the mobo to the cooler. With the ram installed to the board and the cpu locked into the socket I placed the cooler face down on a table with the contact base facing up. Added a thin "X" shape of thermal paste to my cpu's ihs then flipped the mobo upside down and lowered it onto the cooler making sure to line it up. Then I tightened the mounting screws a little at a time, moving in a diagonal pattern from top left to bottom right, top right to bottom left and back and forth until they were all tight. It helps make sure that the cooler mounts evenly to the cpu. Trying to mount the cooler by holding it in your hand with the motherboard on edge in the case and accessing the back of the mobo through the tray cutout in the case is really difficult because of the bulk and weight of the cooler.