I would say it should be fine to use, since the most likely scenario is that it's just one of the fans causing a bit of noise. If it was a more serious type of noise I'd agree with Saph not to use it but in this case it's such a minor noise it shouldn't be any issue so long it doesn't get worse.
It could be something as simple as that it's using auto-controlled fan speeds using PWM (4-pin connector) and has set itself to a certain fan speed that, with the specific fan, causes a bit of air turbulence, which leads to that sound. How close the fan is to as well as the shape of the fan grill are two major factors for this effect. One of my fans makes a very similar noise at 23%, for example. And if this is indeed the cause there's nothing to worry about; it's normal and caused by the exact same principle that makes whistles and flutes work!
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As for the front jack noise; Is this heard from the PC or through your headset?
If it comes from the headset, that's unfortunately normal behavior. Front panel audio jacks are generally quite a compromised design and very prone to electrical interference (the same reason why antennas work). This is why many will recommend you use the port at the back instead of the front.
If it comes from the PC, however, it may be more serious. It's hard to diagnose simply based on description but could be anything from a harmless coil noise from the built-in audio components or graphics card or it could be something more serious such as a grounding issue. Might be as simple as checking the cable connection or unplugging and replugging the cable to fix this.
Regardless which one it is, using the port on the back seems to be enough to eliminate this issue as you said. Other possible solutions would be to move around the internal cable to eliminate possible interference or ground loops, though it may require a full replacement of the front audio port or simply a better motherboard. (Pre-made computers are known to not always use the greatest quality of components).
Hope that helps!