Vibration noise

I have a 2001 ford explorer xlt. It has 110,000 miles, but has been well maintained. Recently, an ear piercing sound develops at 40 miles per hour. The noise stops when I past 40 mph or fall below that number. Any idea about what this may be??

I believe 40 mph is the speed at which the torque converter lock-up engages and disengages, depending on whether you’re accelerating or decelerating.

I’ve heard of unusual vibrations from a malfunctioning lock-up, but never an ear piercing sound.