Normal with bluetooth devices. Very faint though. Much more noticeable if you have a physical external bluetooth boombox/speaker - annoying as heck. Basically, the speaker goes into standby mode to save battery, but if you do something that requires sound it pops as it activates and makes sound until it again goes into standby mode.
I just got my first pair of AirPods yesterday and noticed this yesterday - I haven't had it happen at all today. Yesterday, I noticed it when listening to music and starting up the camera - I'd get a tiny pop - not sure if camera's activating the airpod's mic or something like that.
Having used Bluetooth speakers for 5+ years, this is far less bluetooth pop than with other devices that I've had so ... doesn't bother me.