christianh wrote:
Im especially thinking of the Noctua fans but i've heard pwm fans give a ticking motor noise from the pulses is this right?
It's not that simple.
There are two main kinds of fans: 3-pin and 4-pin. The 4-pin fans are generally referred to as PWM; they use the fourth pin to control the speed using a PWM signal. 4-pin fans do not click. Since 3-pin fans don't have PWM built in, their speed is controlled by the average voltage of the "+12V" pin. Some of these fans click when controlled by some motherboards.
There are two main kinds of fan control: voltage and PWM. All 4-pin motherboard fan headers use PWM, and a few have the option of using either PWM or voltage control in 3-pin mode. It has become very rare recently for motherboards to support voltage control in 3-pin mode; the controller chip that has come to dominate the market uses a modified PWM scheme.
That's where the clicking comes from: modern 3-pin fan controller chips use PWM rather than analog voltage control to vary the fan speed, but that screws up the speed sensor on a typical 3-pin fan. To compensate, the controller puts out a full-voltage pulse a few times per second, which causes a sudden torque change in the fan, which makes it click, but also makes the speed sensor work correctly.
Bottom line: If your motherboard has enough 4-pin fan headerss for your needs, use 4-pin PWM fans, even though they are a bit more expensive. If instead it has lots of speed-controlled 3-pin fan headers, go ahead and use 3-pin fans, but expect some of them to click. Most brands have a lot of sample variance in the clicking noise, so just buy one or two extra fans and use the quiet ones. A completely different alternative is to use a voltage adjuster such as the Zalman FanMate, which never results in clicking, since it is totally analog.