The DL380 G7 is pretty quiet all things considered, just be cautious because sometimes if you add non-HP hardware it can force the system to run the fans at 100%. This also happens sometimes if running non-standard kit in the PCI slots.
I ran a Firepro S9150 once and it made the fans run at 100%, not a problem as it was in my basement, but if it was in a living area, yeah its like a jet taking off haha
I know some HW can force the fans to go full speed, specialy video cards. About the noise, my brother is using it as workstation/PC. It has 2 E5620, 32GB DDR3 and a GTX 650ti card. Even in games, the noise is decent.
About "jet engines", Have you heard a C6100? The noise of the fans is horrible. It has 4 fans at some huge RPM.
Cool, although there was a HP issue where if you didnt use their preferred 2,5 Inch drives it throttled up the fans... very annoying. Wow, what an cool setup as a PC, I'm surprised that its not unbearably loud to be honest, but I try to make all my PCs as quiet as possible haha.
Havent heard the C6100, but their notority preceeds them... Although I guess thats what you get for something with such a massive density of CPUs. It would be nice to own something like that one day haha
The HP works just fine. In idle it was very quiet. More like a whisper.
I am aiming to a bladecenter(HP or Dell). From what I see, Dell has a greater density. With quarter blades with 2 CPU/blade. That is 32 blades, 64 CPUs in total.
My ultimate goal is to get to 1000 cores. First step, then the sky is the limit.