My guess is tires, but that's just a guess. If you have any low noise pavement around you can test drive on that (we have that here in Seattle in certain areas, quite remarkable stuff). Of course the DOT would rather spend millions on concrete sound walls than thousands on low noise pavement... not that I am bitter...

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra