1999 Lincoln Cartier Towncar 158,000 V8 - starting at 30 mph a low humming noise begins and increases in pitch as speed increases. But only when depressing the accelerator. When you 'coast' the noise disappears. One mechanic said it was tire noise but there is no noise except above 30 mph and only when you 'give the gas'. And I can't tell exactly where the noise is coming from - front or rear or middle of car.