Retina MacBook Pro Fan Soft Beeping

I've noticed that if I lean in close to the right side of my Retina MacBook Pro Early-2015 13" model (where the fan is - between the "0" and "-" keys) I can hear a soft, irregular beeping from up to ~3-4cm away. It appears to only happen under low-load conditions (eg: when there is no CPU-intensive tasks running). I am pretty sure it is just the normal sounds of the fan running at low speeds, but better safe than sorry.

You cannot hear the noise when the fan speeds up (i.e.: compiling code or gaming), and I have used a little bit of "canned air" to see if that got rid of the noise, but to no avail in addition to powering off the laptop.

Call me a bit of a worrier, but it has served me well with laptops in the past. 😉

Is this normal behavior of the MBP or should I be concerned and call Apple Support? This did not happen (from what I can recall) with my 2014 MacBook Air.

Note: I would post a recording of it here, but it appears to be to quiet to be picked up by the iPhone's mic.