Seagate Barracuda or WD Green

The green will run cooler and quieter...and slower. The Barracuda will run faster and hotter and louder (but not all that hot or loud). Basically, they're not comparable drives. You might consider a WD Blue instead - it's pretty much in the middle.

I've got two 3TB Barracudas in my daily driver and they average 32C-33C. If they're working hard and I have the side panel off, I can hear them, otherwise I can't.
 
Solution
My WD Greens run about 1-2 degrees cooler than the 2TB Barracudas they sit next to. The Barrcudas are actually quieter and they are nearly twice as fast, reaching burst speeds over 200MB/s and sustained transfers between 145-160MB/s.

I've had 4 of the Barracudas in my server for 18 months. Barracuda all of the way.