If this chick is not growing as quickly, you can gently squeeze the crop and listen for crackling, look above and slightly behind the right shoulder for a bubble under the skin. If thereās a bubble, it has a ruptured air sac, which can be fixed by piercing the bubble, there are some threads on BYC about it if you search, Ive found treating it to be hit or miss, but the earlier you catch it and relieve the pressure, the better chances there are, but you have to watch it after because it may need to be repeated every so often for several weeks. Iāve had 3 like this and 2 died, but the first I didnāt discover until the chick was really far behind, I had never heard of it to check for it. This is the only experience I have with crackling or tapping noises.
which is his gf 
and the babies with no mom have a black beer and a dragon neck pillow, stuffies really help they cuddle under it and calm down
