Looking for a quieter Ender 3? Then get yourself some silicone pads. These are used on record players (remember those?) to reduce vibration.
I thought if they reduce vibration on a record player, then they should work just fine on an Ender 3 printer. And guess what? They work perfectly! Vibration on the table I have the printer on was reduced by 90%. Perhaps more importantly, there was fairly significant noise reduction as well. Really, that was my aim. I wanted a quieter printer first, followed by vibration reduction. Now all I hear is mostly fan noise, the hotend in particular.
They’re 1" diameter stick-on pads. 1/2" high.