I have a major highway behind my backyard. The noise has increased dramatically since a 60' tree in the backyard has died. The exterior wall consists of 2x4 framing and R-13 insulation; outside-7/16" OSB and hardiboard, inside ridgid foam panel and 1/2" gypsum board.
Should I replace the aluminum windows with another type window? Should I insulate etc. the 4' crawlspace under the house? Any other sound deadening suggestions?