Agreed, this is an excellent idea. Even a few feet of flexible PVC works wonders. I have also dangled my pump just above the bottom of the sump so it’s not touching anything. Then add a flexible line and it runs real quietWhat is your return line made out of? If it is all hard PVC, vibrations will definitely make it louder. I recommend using some clear vinyl tubing from Lowe's directly from the pump, transitioning to PVC after 8 inches or so.