If memory serves the fan we used was a few mm larger overall but the screws fitted, the thickness was the same.
As I type this I have four DNS-320 less than a metre from me working on backing up our servers. I know they are working because the disk LEDs are flickering and I heard the disks spin up some time ago. I'm not saying that you are wrong about fan noise, you are just unlucky and have a 'lemon'.
I don't see why the fan you are looking at shouldn't work, just be careful when you wire it up. Also that fan is no where as expensive as the one we used but when the client wants the unit fixed 'yesterday' as opposed to cheaply you use what is to hand.