Some crossbows are far louder than other Less expensive, cheaply made crossbows tend to be noisy Others like, Excal, TenPoint and Bowtec are less noisy The noise will only make a difference if the bow doesn't shoot fast, the deer is on high alert or the distance is too far.
You are up close and personal when you shoot and nthe deer is 20yds or more away If the deer is relaxed by the time the noise registers it is too late as the arrow had all ready gotten there