front end noise 2001 honda accord

Over the past three weeks, my 2001 honda accord has developed a humming sound heard especially when coming off the freeway at 45-65 mph. It does not vary with turning the wheels, applying the brakes, shifting into neutral, or rotating the tires. While it sounds like the left front, it could be either left or right. Streering stability is unchanged. No ABS light has come on. NTB checked the usual components when rotating the tires and found nothing wrong. Disc brake pads had plenty left at time of last check at 37500. The only thing left that I can figure is something amiss with the ABS sensor hardware, eg., the tone ring, etc.
Thoughts?