Bought an Ender 5 plus a long while back and noticed when I first bought it that it was very noisy both for fans and stepper motors. First mod was the silent motherboard, made a big difference but still too noisy. Next was to replace the PSU fan with a 120mm fan, had to print a new cover plate, it does squeeze in there honest. Printed some extension feet to lift the machine up for better cooling. Bigger/thicker/slower motherboard fan as that thing is a screamer. Not impressed with the Bowden tube setup so replaced that with an NG Micro Swiss direct drive extruder and used the Bowden tube as filament guide, not necessarily quieter but more reliable. Stiffer bed springs, much less levelling required. Added a Sonic Pad to replace the Marlin touch screen, no LAN/WiFi was doing my head in. Ditched the glass bed with bulldog clips and replaced that with a magnetic pad and PEI build plate, much more reliable prints and no problem with PETG sticking too well with PEI. The glass stuck too well and ended up chipping the glass hence going for PEI. Added bracing to all the corners as 2020 in that size frame is a little wobbly. Added WobbleX and Delrin leadscrew nuts as it did develop a squeal on the Z axis, WobbleX also gets rid of the leadscrew ringing vey well. It is now a quiet, reliable, acceptable printer. Might think about linear rails next. Not going for Core XY upgrade yet as there will be too much downtime for a machine that is used daily. How to turn a £500 machine into a £1000 machine might be the lesson I learned.