| Noise is my main concern. Currently the subfloor, which we painted and
| had bare for some time now, is squeaky in spots. I plan to walk
| throughout the entire floor and add some screws to those squeaky areas
| prior to installing the hardwood floors. Then a co-worker stated the
| barrier can also serve as a noise suppressor, thus, leaving me to wonder
| if I should still add it.

If it's solid wood flooring the standard practice is to
use rosin paper under it. (The faded red paper that comes
in 3' rolls.)