Weather Stripping for sound deadening under Fastrack?

From the stories I've heard the best sound deadening for Fastrack is to somehow fill the cavity under the track with sound deadening material.  I finally abandoned Fastrack for Ross/Gargraves on foam roadbed, night and day difference in sound levels.  I can actually hear the sound systems of my trains now.

Filling the cavity with self adhesive foam will be quite a chore; you will be cutting little pieces for weeks.  You could try some foam that is the width of the roadbed but, as John said, the problem is the cavity acting as an echo chamber.  I use Fastrack mounted on celotex tile.  It helps but it is still noisy.  The only way to solve the problem is to get rid of Fastrack in favor of something else, as John did.

I have often wondered if filling in the underside of the roadbed of fastrack and realtrax(MTH) could be done using spray expanding foam. Fill the bottom side with the foam, then after it hardens, use a bare hacksaw blade to level the foam with the bottom of the roadbed. I have been meaning to try this but never got around to it.   I also thought about removing the rail pins and sliding in the correct size diameter of string from a weed string trimmer. Filling the inside of the rail should help quiet it down.

Talk to @Lee Willis, he did a lot of tinkering with Fastrack and killing the noise.  The expanding foam is really messy, and you'll have to trim it after the fact to be level with the bottom of the plastic roadbed.  That's going to be a giant PITA!  I seem to recall that cutting the right sized pieces of foam rubber with just the thickness to fill the cavity was reasonably effective.  I don't know that it'll rival other track systems, but it should cut down some of the noise.

My experience...

1.  Place it on Homasote or Sound Board (same as Homasote just recycled sugar cane fiber).

2.  I Used the densest sound deadening carpet pad I could purchase from Loews's... it's about 1/2" maybe 5/8" thick.  It was easy to cut and place inside the track with a nice big set of scissors... it's also easy to remove.  You want it snug... but, don't drive yourself nuts ...it takes about 5 or 6 pieces to get the routine down then it's not all that bad to install.

It cut the noise level significantly... however,  I came from Super-O and it was still not as quiet as Super-O.  For that and several other reasons... I went with Atlas.

My cheap ($10/roll) and easy to cut roll of foam works pretty well. Plus, all you have to do is put a section under the track and screw the track down. Peace of cake. I can enjoy the sounds of my locos and the pleasant clickity-clack of the wheels on the rails.

My layout is built with Fastrack. The base of the layout is 1/2" plywood, covered with the styrofoam sections sold at Lowes / Home Depot that are used to insulate garage doors. The foam is very dense and provides a solid surface that is quiet and can be customized easily for depressions in your "terrain", bury wires "below grade" to be covered with landscape material...and trees can be planted by simply poking the trunks into the "earth". And most important: you will hear the sounds of your trains.

You will need a long cabinet screw to anchor your track through the styrofoam to the plywood down below. I found these specialty screws at Ace Hardware. Be careful when screwing into the plywood to avoid too much pressure that will cause a dip in your track work. The video is "proof of concept".

HTH!