Weird noise too

I have a 2000 Park Avenue with 113,000 Miles on it. On a trip back from Nebraska, my car started making a humming noise while in motion. The noise did not increase with speed variation fast or slow. I had thought maybe it was the road itself, due to new construction, but didn't change when I was driving on an old section. I drove over 400 miles with the noise, stopped several times, checking under the hood and around the vehicle. There were no dash warning signals, no vibration, fluids all checked okay and tires and exhaust, no play in driveline. I am unable to determine by driving the car as to where the noise is coming from. The car runs fine otherwise. Anyone have any suggestions other than turning the radio up louder. Thanks

Well, with the help of friends I found out the right front wheel bearing was going to the great beyond. I replaced the front hub assembly and the noise disappeared. With the front wheels off the ground and in neutral I couldn't feel any dragging or noise. Cost me $147.02 for a new hub assembly.