You have noise down the drain lines because air is being drawn down the drain along with the water. A gate valve is used to very closely match the rate of drain to the rate of output from the pump. When these 2 rates match, the drain line stops drawing air in, and laminar flow is achieved--or "full siphon". That is what makes a drain silent.
Hey so I used some of your advice I have made the drains nearly silent with fully subversive drains with a ball valve attached to each line. The problem I'm having now is I can't exactly match the drain rate to the return pump rate. So I am either slowly on the way to overflowing the display tank or slowly on the way to overflowing the sump depending on which way I turn the valves. Please advise
Before you constrict your drain line with a valve, I would stongly advise you to have a backup drain line or you'll eventually flood your house.
Do yourself a favor. Read all about Herbie style overflows, have a plan, understand the flow rate of your pump compared to the rate that your drain lines can drain water, and have a dry/almost dry backup drain that can handle the full output of your pump.
Unless this tank is in your garage and you don't care if it floods.