how much of the noise is vibration transfer from the server to the table?
Also, other than the CPU fan(s), look at tearing out ALL of the 12v fans in favor of externally powered 120 vac fans. You can get some high-volume quiet airflows from QUALITY 4" and 5" muffin fans that are 1" thick (or less).
By pulling the fans off your server power supply, you will be saving around 10 watts per fan. You will gain head room on the power supply, lessened stress on the p/s, and lessened DC motor noise being backhauled onto the 12v DC power lines.
Mount the external 120 vac fans with thick rubber mounts for vibration isolation. You want fans pushing air into the server and more fans pulling it out.
Your air intake should be at least 12" up from the floor.
Side note; in most data centers, high-density racks will pull air from below the floor and exhaust it out the back and top of the racks. I'm not talking converted closets or offices here.