These are the most amazing fans for their tiny size (40mm) 5,000RPM at 3,500 RPM silent : r/Noctua
5v/12v/24v Quiet Hot End Cooling Fan Super Silent Fans 40mm For Ender 3 5 Pro 4010 3d Printer With A 2 Pin Jst-xh Connector - Pc Hardware Cables & Adapters - AliExpress
Silent Fans for your PC from be quiet!
Coolerguys 40mm(40x40x10mm) 12v Ultra Quiet Fan CG4010L12S for SY12401
Amazon.com: 4 Pack 4010 Fan 40mm 5V Dual Ball Bearing Brushless Quiet Cooling Fans for 3D Printer Ender 3 Pro (40mmx40x10mm,2PIN) : Electronics