I replaced an old AIO with this one 2 weeks ago and i got the same noise. When the Pc is straight (Corsair logo looking to one side), i get the noise.
If i tilt the PC towards the logo, so it looks to the bottom, the noise increase.
If i tilt it so the logo face upwards, 0 noise. I tried to dismount it, and move the pump and radiator freely while the pump was on to try to move the air and nothing.
Radiator is mounted on the front, vertically and with the pump hoses on the upper side.
Could it be a faulty pump?