Same here. I watercool for silence as well so generally run my fans at lower RPMs.Same, I run at a touch below 40% for this reason. I find D5s have a higher-pitched hum at middle speeds which is quite audible to me (it seems like this frequency actually becomes less noticeable when running at 80-100%, although then it makes much more noise in other frequency ranges).
I do watercool for quietness, so my fans are always down. That may be a big difference in the perception of the D5 noise.
I have a non-XL regular O11 Dynamic and can hear the pump quite annoyingly at more than 50%. I generally run it at about 35-40%. For comparison, all fans in the case are run at 1000 RPM.Lian Li O11 Dynamic XL. Where I'm sitting right now I wouldn't even have to use my full reach to grab the pump if the glass side of the case was removed. My fans are ML120's currently running at 1100rpm, and they're the only thing I can hear. I can hear the pump on startup as it spins up, if I'm really listening for it. That's the only time I even notice it's on.
I did notice during testing, with my pump just sitting on a table, that it can cause very loud chatter against whatever surface it's sitting on. All I had to do to stop that was pick it up. It was the mount vibrating against the table. I believe a standard mount screwed into the case will likely vibrate something. Mine is isolated with rubber washers. And I'm using the mount pictured below. Seems to hold the pump more securely than a side mount.
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Not true.If the pump speed is 2 low the water will sit longer in the blocks (we dont want that) and if it is too fast it wont have enough time to remove the heat.