Sound considerations IME:
Sound is usually based in movement with vibration/friction. Any panel which reduces or eliminated movement will attenuate the sound. I found Advantech 4' X 8' X 3/4" is the best for sound control. Available thru 84 Lumber and other non big box building supply stores. Approx. $30. per sheet.
Tubular rail is louder than solid rail.
Hollow plastic built in road bed acts like a drum, loud.
2 rail trains are much quieter than three rail trains.
Signature scale 2 rail switches are quieter than Atlas 2 rail switches with wider frog clearances.