The 'L'

When I was in D.C. recently I spent a considerable amount of time on the Metro which is the second busiest mass transit system after NYC's subway system and busier than Chicago's 'L'. The thing that I noticed immediately was how quite the trains were. Why can't the CTA use similar wheels and/or track to reduce the noise pollution that currently exists? Montreal's mass transit system is maybe the best from a noise standpoint as they use some sort of rubber covered wheels which makes for a much more enjoyable mass transit experience.