Why does my iPhone ping while charging?

Mine chimes and gives a short haptic buzz when I first plug it in or park it on top of a wireless charger. There is no chime when I unplug it or lift it off the wireless charger.

MagSafe chargers and battery packs for iPhone says this:

iPhone: Place iPhone face up on the center of the iPhone charging surface. Supported models help you align iPhone with the charger, and the charging symbol appears when iPhone starts charging. On other models, the battery charging indicator appears when you properly align iPhone with the charging surface. Unless your iPhone is in Silent mode, you hear a chime when charging begins.

If yours does it more than once, you may have an intermittent power connection, it may be misaligned with a wireless charger, or have a defective charger or cable. It may be thinking you are unplugging it and plugging it in repeatedly while you think it's still charging.

In between the chimes, does the battery icon in the top right occasionally turn white (instead of green) with no lightning bolt?