Is the noise being reduced if you touch individual case panels (side, top, back front) — that is, firmly press against a panel? If yes, then the respective panel is "resonating" with fan vibrations. But as you are saying that the noise level is independent of fan speed, I doubt that this is what is going on. Because resonance of parts of the case would be limited to a somewhat narrow band of frequencies. It would happen if an natural frequency (eigen frequency) of the case component is close to the rotational speed or to a multiple of the rotational speed of the fans.
As I said, these rubber pads are just for show. They neither help with isolation nor with dampening. The fan frames are bolted to the radiator casing, and this bolt connection is rigid. Any fan vibration is practically fully transmitted through the bolt connection from fan frame to radiator casing. This is a common issue with all fan mounts in watercooling kits which I have seen.
*However*, at at this point it occurs to me that it is more likely that the fans make the noise themselves, not exciting case parts, as argued above.
According to Corsair's web site,
- the case comes with "CORSAIR AF RGB ELITE PWM fans",
- the closed loop liquid cooler comes with "CORSAIR AF RGB ELITE fans" too.
So they seem of identical type.
But why aren't the case fans making noise, but the radiator fans?
A few possible reasons:
- They are not the same fan type after all.
You could unmount the fans and look if they have nameplates or anything which could provide further hints on this.
- By coincidence, the case fans which you received happen to be good quality and the radiator fans which you received happen to be bad quality. Most fan makers have widely varying quality in their fan series. Buy a dozen fans of the same series, and you get some good ones and some bad ones.
You could swap the case fans with the radiator fans to find out.
- The flow restriction which the radiator fins and the case's top grill create make the fans noisy, unlike the flow restriction from the case's front panel.
That's harder to test. There are special spacers available with which fans can be mounted slightly further away off their original mount, in order to reduce aerodynamic interference between rotor and grills/ fins etc.. Respectively longer screws would be required to use such spacers.
However, this type of noise is more prevalent with fans which are mounted in "pull" mode, whereas your radiator fans are apparently mounted in "push" mode.
- The fans work well if mounted vertically but bad if mounted horizontally, notably with hanging rotor.
You could test this simply by laying the case flat on its right side. Then, not only the case fans but also the radiator fans are mounted vertically.
Uhm, they may be expensive, but they are just Corsair fans. Their being expensive doesn't necessitate that they are designed well, manufactured well, and subject to tight and consistent QC.
(But the other way around is true: That fans are designed well, manufactured well, and subject to tight and consistent QC, absolutely necessitates that they are expensive. This cannot be done cheaply.)
That is, you identified that it's really the fans, --> not the pump <--, right?