The sound doesn't increase if you don't get louder fans. They help immensely. http://www.newegg.com/Product/Product.aspx?Item=N82E16835352007
These are the ones that come stock in your case, and while they are good fans, you can get better for cheaper. Luckily your case supports 140mm fans, which are quieter while pushing more air. http://www.newegg.com/Product/Product.aspx?Item=N82E16835242011
These are slightly quieter, so the noise level will not go up, but they push a bit more air, so you can just get two of those, and have one exhaust in the top, one exhaust in the back, and intakes on the front and side. Ideally you want two intakes in the front, two exhausts in the top, one in the back, an intake on the side, and an intake on the bottom, but that would mean buying 5 fans. Generally I recommend at least 3 fans.