There is no gainsaying it, the Delta 38 cfm is L O U D. But wait, there's more. The particular sound it makes is the most annoying I've ever heard from a PC case.
Nonetheless, I use one. It's a mind over matter sitch. After hearing the Delta monster for a few months, switching back to a YSTech 27 cfm temporarily is a real treat. Nevertheless, the YSTech becomes annoying after a couple of weeks. Pabst fans are said to be pretty quiet, but finding one in the US seems a bit difficult. Delta now makes a 30 cfm CPU fan that's said to be more bearable than its monster banshee from hell model. If you really want a high performance OC'd box that's genuinely quiet, it means a good bit of time and effort in sussing out the best materials and methods needed to achieve the "impossible." A thermal monster that's cool running AND quiet is no mean feat.