) Whenever it is on. When it's not doing much, the noise toggles on and off, but when its doing something, such as playing a video (the I played video in my video of the etching is muted) it becomes more constant. Is this an unhealthy noise or just a normal noise? The noise is very quiet, so you'll have to turn up the volume to hear it.
A Dell Inspirion 7586. I've noticed that if the computer is inactive for an hour-ish, the etching becomes far less constant, only happening in a few seconds burst every 30-ish seconds. May be a coincidence, though.