The RIR looks kind of bloated, possibly the ticking sound is lung congestion from pressure of the swollen gut on the diaphragm. It is hard to say exactly what went wrong, you need a thermometer in there with them and need to monitor the temp in a poorly ventilated garage. I myself don't like medicated feed and refuse to use it due to poor experiences with it, but can't say that is what is wrong here. My bad experiences have been from overgrowth of microbes unaffected by the antibiotic in the feed, which causes digestive problems due to this microbial imbalance. As to the crop, it is what you might be referring to as the stomach, is located at the end of the esophagus in the neck and can be palpated easily at the front of the bird below where the neck connects to the body. You can feel food in there after the chick eats and can also visually see it bulge when full. It should empty out during the night while the chick sleeps which is why you can only check to make sure it is empty by palpating in the morning before the chick starts eating again. The whole picture presents a pretty good recipe for a case of bloat. Too hot, poor ventilation, medicated feed, microbial imbalance, leading to excess gas and bloat. What kind of antibiotic is in the feed, anyway? Since I never use that stuff, I'm unfamiliar with any of it. Hopefully, this will resolve on it's own... Not sure you can use simethicone for chickens, but you might be able to find out by doing a forum search. I would isolate the affected chicks just in case they have something contagious and make sure they are not exposed to excessive temps. Monitor the crop for emptying in the morning(gently). Some people feed yogurt to help sour crop and some swear by apple cider vinegar to prevent it, but sometimes it is a mistake to do too much, especially in a chick this young, if there is a chance that it will resolve on it's own. It is hard to advise on so young a chick that one can't really see or examine yourself. Most likely a little yogurt (plain) won't hurt, though and may help restore some microbial balance. And don't think I would worry about drafts in 100 degree weather, unless there is a sandstorm blowing up out there... The tank you have them in will protect from drafts anyway. Birds are also sensitive to pollution such as carbon monoxide gas, in an enclosed garage, if you are still parking the cars in there. Do hope your chick is doing better!
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