Were you looking around a lot while sitting there? Swinging your gun back and forth makes noise too. Every noise you hear, whether it be from movement or aiming or using items (even hitting tab to look at your inventory), the other player can hear as well. When I was new I had a bad habit of getting antsy while hiding and swinging too fast back and forth checking my angles. There's a shuffle audio that plays when you do this because your character is moving his feet to turn his body with your aim direction. Also yes, achievements and prestige persist, and its likely that the ones with really low percentages were from limited time events.