internal sump return pump vs external?

[Aqua Man]

I have two set ups one of each. I have taken notice of them after reading all of your posts.

My in wall tank is a 100 gallon custom with a 65 gallon 3 stage sump. I run 2 3/4" returns with line loc which is powered by 2 seperate MagDrive1000's pumps. Generally quiet and virtually indestructable these pumps do put off mild hum.

My coral breeding tank is a 300+ gallon custom with a 100 gallon 6 stage sump with a natural plant refuge. I run 2x 1" returns with no line loc which is powered by a single massive external Dart 4700 gallon/hr pump. I cannot hear a sound from it! Absolutely no noise, I do have it screwed to a chunk of 2x8 which is PL4000'd to the cement floor. I did however level it in both direactions, this may be why. As for the heating up comment, I put my hand on it and it was ice cold. It has a section that throws cool air, but the impeller housing may heat up, not sure.