My dad put a new bow string on my hoyt. How many arrows does it take to
stretch the string out. When I had my other srting on the bow the
bow was quiet as a mouse. When I shot it with the new string on it is louder than the last
bow string why is that.

It depends on the string materal but usualy a few hundred shots will get it close. As for the noise, I don't know about that one.

SF

Ditto on the last comments...in addition, strings that are made of material that does not stretch or does not stretch much generally are louder as they do not absorb as much energy as strings prone to creeping.