Noise depends on the cooler. You can download GPU-Z. It allows to monitor GPU temperatures, fan speed, etc. It even allows you to log them into a file. Check at what speed your GPU fans are running. You can also control fan speed at Nvidia control panel. Use manual fan control and reduce the speed. See if it makes less noise at idle. Are they both making a lot of noise or just one of them? If they both do, I guess it is just fan designed that way.