Yes, by installing an aftermarket cooler you will likely void the warranty. What are your temperatures? If they are acceptable you could set up a custom fan profile that would lower the fan speeds according to the temperature. So the card would be less loud, but at the cost of higher temperatures. Also how is your case airflow?
Hope this helps!
its 86 C heavyload with fan at 60%. and 34C at ideal with fan at 30%. Case air flow is terrible but scine its the mid-tower, i cant do nothing else ...