Doug;
One thing not often mentioned.
Cars like Reefers and Boxcars and loaded or covered hoppers act like speaker cones for the noise.
Put a block of pillow foam or some such in them and the noise level will drop quite a bit. The walls of the cars resonate to act like speakers. Foam stuffed in there will damp them out.
Track wise I'm putting WS foam roadbed under my Scaletrax on the new layout. The old one was Realtrax and had carpet under some of it. The rest had Sound board under it. that was less cost at the local Lumberyard than Homosote and damped more sound.
I'll be doing all these things to damp rail noise and make the sound fade better as the train moves away.
The Den / Christmas layout is still Realtrax and I lay green felt (farmland) or Quilt batting (Christmas snow) under it. This reduces the noise some but not enough for the main layout due to much increased size and therefor more speed on the main layout.