I too experienced the same issue shortly after installing the MasterLiquid 120 lite CPU Cooler. Have you tried checking your motherboard fan settings in the BIOS? I found that the MSI motherboard that I'm using defaults the CPU and pump headers to use the PWM mode (with 4 pin plug). From what I found in other forums, the pump on these coolers (with 3 pin plug) need a steady supply of power so you want to set the pump header to use the DC mode. After updating the pump header setting, I verified that the other fans were set to the correct mode, saved changes and restarted. After that, all was nice and quiet. No more noises from the pump and the CPU is nice and cool since. I hope this helps.