These are the most amazing fans for their tiny size (40mm) 5,000RPM at 3,500 RPM silent : r/Noctua
Office Depot
Prusa i3 MK2/S Adaptor for 40mm Silent Fan by Area51 | Download free STL model | Printables.com
Silent 5v 12v 24v 40mm Cpu Dc Cooling Fan - Buy Silent 40mm Fan,5v 40mm Fan, 40mm Cpu Fan Product on Alibaba.com
Mayitr 1pc 40mm Super Silent Cooling Fan 24v 3d Printer Fans Cooler For Ender 3/ender 3 Pro/ender 5 - 3d Printer Parts & Accessories - AliExpress
Amazon.com: GDSTIME 2-Pack Quiet 40mm USB Fans, 5V Mini Brushless DC Cooling Fan for VR Gear Aquarium Router Playstation Raspberry Pi Helmet Ventilation : Electronics
PROCOOL AV Cooling Solutions - More Air with Less Noise
Delta EFB0412LA 4cm Best Silent Quiet 40mm Fan 4010 12V 0.08A Cpu Comp – COOLINGFANSTORE
40mm Silent Cooling Fan 12V 2Pin 4010 for Brushless Quiet for PC Computer for | eBay
40mm Silent Series Cooling Fan
Farfi DC 24V 40mm Ultra Silent Cooling Fan Cooler Radiator for 3D Printer Extruder CPU - Walmart.com
Raspberry Pi 4 - 40mm Fan Comparison - Martin Rowan
MakerFocus 3D Printer Fan 24V 4010: 4pcs 3D Printer Cooling Fan 40mm Quiet 0.08A DC Mini Silent Brushless Fan 2 pin for 3D Printer, DVR and Other Small Appliances Series Repair and Replacement
Coolerguys 40mm(40x40x10mm) 12v Ultra Quiet Fan CG4010L12S for SY12401