BA23 fan noise

Hi, I've been messing around with my PDP11/83 and a Microvax, both in BA23 boxes here. These fans make too much noise for my home office area, and I cannot possibly need the original airflow. Even with the internal jumper set for 10V to power the 12V rated fan motor, these are still noisy. It's not even just the noise of the air moving, but largely a whine from the fan motors. One box is worse than the other with the wine. I've unplugged the front fan, since instead of spinning drives I have solid state CF cards and SCSI converters -- no heat in the front of the box at all. I have some 24V fans in my junk box that fit and make almost no sound at 12V, but at half voltage might not move enough air to keep the power supply, CPU, memory, SCSI, and ethernet boards happy. My guess is so long as there is some air movement over the boards, the biggest issue of concern is cooling the power supply. Does anyone have any suggestions for figuring out how much airflow I actually need, and achieving it with either stock fans at further reduced voltage, or some kind of replacements? I don't need an accurate solution, or something with complicated compensation for varying temperature, just something quieter, moving less air, but still enough air. Mark -- Mark G. Thomas (Mark at Misty.com), KC3DRE