I have used two Shuttle XPC for the past three years. One of these ran SME 24/7 for 32 months. Never had a problem. I bought these as bare bones units; these days Shuttle offers a server line but I haven't tried them.
I did upgrade the fans to models with lower db, and installed vibration pads on the mounts. That was a major improvement, sound wise. I also use Seagate Barracuda 80 GB drives. While not the least noisy you might find, they are within my tolerance and have been reliable.
As an aside, one thing I want to try this winter is to load SME on a Mac Mini and see how it fast it boils the drives.