I have a 95 Ford Explorer, just recently it started making a humming noise (seems to come from the engine) which gets louder as the speed goes over 20mph. It's loudest @ 35mph & then quiets a little when it hits 40mph. One mechanic said my tires needed an alignment. Did that & still have the problem? Any ideas? My car has about 135,000 miles on it.

Did the mechanic rotate the tires also ? You might try that. Can you make the noise go away by slightly steering it back and forth? If so it could be a wheel bearing going bad.