Iâ€™m curious what w/c set up do you have?
I have re-built my w/c machine countless times. I turned so sick of managing everything that now, after four years of enthusiastic experimenting, I've bought a new computer, completely air-cooled.
The old computer is an AMD 2600+, Radeon 9800, Seagate Super Silencer 400 with Nexus fan, Raptor and two Samsung spinpoint V (5400 rpm) for storage. Blocks and one rad Innovatek, one Black Ice, Eheim 1048, 12/16 mm aquarium tubes. This is squeezed into a G-Tower alu case. It sports one 120 mm blow-out fan in the back and one on top. Every inch of the case is sound isolated with the type of heavy sheets used in cars and machine isolation.
The water line was split using two T-joints. The "straight" line fed cpu block and a rad.
Second loop fed gpu block and rad 2. Almost as much water as the cpu.
A small volume of water passed an outer line, which made many turns but still had to be clamped to adjust flow. This outer loop ran along aluminium profiles of the type used in party tent constructs. The alu profiles were glued, with thermal glue, to big copper plates glued on (the inside of) top, back and bottom of the alu case, heating it up as the water got warmer. It actually worked very fine, lowering temps!
Splitting the water line made a huge improvement in flow. Strangely enough everybody "knows" splitting the line hurts flow, but it's the other way around with a pump like my 1048 because it can manage a very big flow but has poor head pressure.
The Raptor is in a suspended hdd box, but used to be in a home made water cooled sound isolation box. Made for a quiet hdd but water temps had to be kept so low. I tried install a DDC to create a separate hdd cooling line, namely the outer loop along the case. Then the water in the main loop to cpu and gpu could be allowed to go over the ~39 C I needed to keep the Raptor under 44 C. But the DDC noise was almost impossible to live with. I cast my DDC in cell foam and a block of cement and it still sounded more than the rest of the stuff together, ugh. Back to single pump.
The case is dust filtered and together with the rads this made the back pressure too great for the fans to work efficiently at the low speeds I use. The rad fans are sucking air out through the rads at the back and top. I had to use intake fans as well. The rad fans are Nexus 120 @ ~3V. I added a Nexus 92 mm in front and a 4412 bottom intake blowing on the hdds. A paper duct from the back rad made sure a miniscule portion of air is passing the north bridge. No fan goes over 4 V in normal use. That means under 400 rpm. Can go to 5-600 rpm if stressed.
The case feels warm to the touch after half an hour or so. (All w/c systems seem to perform fantastically well the first 30 minutes or an hour.)
The Seasonic sits in its own chamber upstairs and is fed cool air from side vents. Everything is controlled by a T-balancer.
Even though the rad fans are soft mounted with shrouds and everything they still whoosh a little because of the fins. The pump is the most trouble. It makes a noise so hard to dampen. The vibrations of a 1048 are easier even though it shakes like a powerdrill. I suspended it in silicon cords and used soft tubing at inlet and outlet. It can touch nothing solid or everything starts to hum.
Fancy project and lots of tinkering but still not as quiet as my new air rig. Bottom line is that if you can avoid w/c, you should.
Long boring answer, but hey, you asked!
Edited to solve some obvious language problems.