Sources reported Monday that 'Smooth,' the 1999 collaborative effort of guitarist Carlos Santana and singer-songwriter Rob Thomas, has somehow persevered against all odds and continued to receive regular radio airplay this week. 'While the projections of most experts suggested 'Smooth' would fade from the national consciousness within its first year, the song has actually proved surprisingly resilient over time,' noted musicologist Sidney Brown said of the No. 1 single's inexplicable staying power. 'Though it seems not to have any musical or cultural relevance whatsoever, many people, myself included, find themselves humming the track's guitar lick at least once every other week.' At press time, the triple-platinum, Latin-tinged rock record was heard emanating from an estimated 780,022 open car windows and 2,300 department store sound systems. 