I've had my P3S for a few days now, loving it so far. One thing I've noticed is that when I power it on it starts making a light hissing noise. I put my ear up to it and it sounds like it's coming from the gimbal. The noise is only noticeable in a quiet room when the motors are turned off. The gimbal works fine it appears, I'm just worried that something may be wrong. It this a normal thing? Or are they supposed to be completely silent?