Tony,
If this the issue (noisy fasttrack), I had the same issue with our first temporary (fastrack) layout. I tried a few different (unconventional) things. Spray foam insulation into the underside, cutting homasote and vinyl roadbed pieces to fit in the underside, etc. I finally end up deciding on brushing the underside with a thin layer of brush-on liquid rubber (the stuff they advertised on TV to create water seals in gutters, etc.) to create a barrier with the underside parts that carry electricity, and then brushed on a second coat and, while still wet, I pressed in carpet tile pieces cut to fit the underside footprint. I found that this worked best for me in dropping the decibels considerably.
Peter
