Popping Sound, MBP 2016

I have heard a strange noice from my MBP, and am not sure if this is expected or not. Model is MacBook Pro 2016 with Touchbar, 15 inch, Radeon Pro 460, 2.9GhZ i7, 2TB SSD.

The sound occurs rarely, there may be several days or more straight that I don't hear it, though when it occurs, it may happen 2-3 times in a half hour period. There is no association I can make with what I'm doing at the time, so I'm unable to recreate it. The sound is a single hollow "popping" noise, similar to if you slowly squeeze a plastic bottle until it crinkles. The sound is not very loud, but clearly audible, and sounds as if it is coming from approximately behind the trackpad. I've had no other notable problems with this computer to date, have made no modifications to any hardware, or used it in any abnormal way.

I'm not terribly bothered by the sound itself, but I'm aware that the battery is located roughly behind the trackpad, and I worry that an expanding battery might sound like this. The case is not flexed or distorted in any way, there is no abnormal heat being generated, and no smoke, smells, or fumes. I think this is unlikely to be the cause, but is serious enough that I would like an alternative explanation before I disregard it. Alternate explanations might be abnormal activation of haptic feedback, or flexing of internal components as adhesives or seals continue to cure since manufacturing (laptop manufacture date 12-19-2016). The OS X battery status is "Good", "No errors", Simplo model bq20z451, battery manufacture date 12-2-2016.

Thanks for any help!