Reason why pc is very loud when I turn it on then gets quiet when windows loads?

Solution
Usually once windows loads, drivers will take over controlling the fan speed. What you are most likely hearing are the GPU fans. I believe part of this process, is to help reduce dust build up on components by blowing it away, but once all the drivers load they start controlling the fan speeds to more tolerable levels for humans.
Hello... open up your computer... roll a piece of paper up and place one side to your ear... start your computer and search-listen for what computer part is making the loud start-up noise... Moving parts ( such as Fans ) in your computer have bearing surfaces and get dry/dirty causing noise.
 
Usually once windows loads, drivers will take over controlling the fan speed. What you are most likely hearing are the GPU fans. I believe part of this process, is to help reduce dust build up on components by blowing it away, but once all the drivers load they start controlling the fan speeds to more tolerable levels for humans.
 
Solution