The drain adapter is 1" and the pipe should not be reduced. Youe DLFC is correct at 10 GPM. The high velocity through this button will cause noise.
Confirm the DLFC button is installed the correct direction, the numbers should face down.
How often are you backwashing? How long?
In a residential application, every other week is fine, 10 minutes BW, 5 minutes RR is a common setting. You can also change the time it backwashed to the middle of the day so the noise doesnt wake you.