I have an older body on frame car that rides pretty bad and loud. Its got me curious how manufacturers make newer cars ride so smooth and quiet. I’ve done some googling but not found much other than obvious, general things like “rigid construction” and “more soundproofing”. I would love to find a website that goes deeper into it.
There’s plenty you can do depending on what you have.
Swapping in new replacement coilovers, changing out the leaf springs for a 3 link… two trailing arms and a panhard bar.
Make it ride and handle a lot better.
Pulling the interior (seats, carpet, door panels) and trunk liner out and installing Dynamat or Boom mat then putting the interior back together. Spraying the bottom with a Line-X type bed liner. That’ll help with noise and helps keep the inside a little cooler.