WHEN I HIT ABOUT 40 MPH, THE CAR STARTS A LOUD ROAR. ONE MECHANIC THOUGHT IT MIGHT BE A WHEEL BEARING. ANOTHER THOUGHT IT MIGHT BE THE CATALYTIC CONVERTER COMING APART ON THE INSIDE. THE CAR DOES NOT MAKE THE NOISE WHEN IT IS IN PARK AND YOU PRESS ON THE ACCELERATOR TO REV THE ENGINE. THE CAR IS A 1999 WITH 56,000 MILES AND WE BOUGHT IT NEW. ANY THOUGHTS?
If the sound changes or even goes away when you turn one way or the other, that is normally a sure giveaway that it is a wheel bearing.
The fact that it doesn’t make the noise just by revving the engine would make me suspicious of pointing to the cat.
Abnormal wear on tires or defects on tires can also make ugly noise. Can you tell where it is coming from? (Front/rear; left/right?)
Turn off your all caps key - that signifies YELLING.