Jumping the string has already been explained pretty well by others but how do you solve it?
It's simple, you have to quiet that bow down. That "twang" sound is pretty pronounced on some of the superfast bows that guys are shooting these days. The arrow can't soak up all the energy the bow has so some of it is either absorbed by the bow it'self (why we don't dry fire the darn things) or is released as noise. Most bows already come equiped with string leeches and other noise reduction equipment but aside from that the easiest ways to reduce the noise is to not use such a high draw poundage and using a heavier arrow.
A lower poundage will quieten a bow down because it won't have as much excess energy after the arrow is shot. A heavier arrow is able to soak up more of that bow energy as it's being shot. Trust me, 70 pound bows are overkill. You don't really need more than 45 pounds to get a complete pass through and kill a deer. A heavier arrow penatrates much better than light arrows because it has more kinetic energy.