ooo I am also looking for a return pump! Eheim is da best?
All of my Eheim equipment is dead silent, external or internal. Sorry for not noticing your question.
At night when I'm trying to sleep, it's the computer I cuss at, not the tanks.
Also, the external and internal "versions" are the same...no difference or different part number. Just no water around it when use externally to muffle sound.
If you're going to use some Korilias for flow it shouldn't matter that much if the flow is cut back some on the return from your sump. ;)
Todd
Killed my first coral in 1991, have tried to do better since. Always tricky.