Sometimes black spokes make a noise from the crossing. The coating is a bit rough I guess and until it rubs smooth the spokes can make a noise. Pinging on a newly built wheel can be from spokes unwinding. If the wheel isn’t “stress relieved” after building riding will cause the tension to decrease which allows the spokes to unwind and ping. There are various valid methods to stress relieve. Squeezing spokes, flexing the rim sideways, walking on the rim in socks. They all do the same thing. Momentarily removing tension from a spoke to allow it to unwind itself. With bladed spokes you can see the wind up and take it out while building with a spoke tool. With round spokes you can feel the spokes wind up if you put your fingers on the spoke while tightening or loosening a nipple, then go the opposite way to take out that wind up but that isn’t very accurate so you still want to stress relieve.
I’ve noticed on my own carbon rimmed wheels that spokes will ping after a season or two even when tension is still up to spec. No idea what causes that but I’ve rebuilt wheels like that with new spokes and the noise goes away.
I always build with something to lock the nipple threads. Just oil will allow the nipple to unwind when I get a bit squirrelly and side load a wheel. Some builders say that just oil is fine and that a properly tensioned wheel can’t lose tension when riding normally. I say, define normally? Mountain biking is way more harsh than road riding. I say lock those threads with something.