Mazda 5 Manual transm. - There is a front end humming sound only at certain speeds (45-50 mph and then again at 65-70mph. Are there some likely causes? Rotated tires, checked front wheels for play and seemed OK.
Noisy front wheel bearings are common on any car. They sound like an airplane engine. Often, but not always, the sound will change when turning slightly as in when changing lanes. It can also sound like it's coming from the right side, and it will be the left one that's noisy. The only way I found to be sure is to run it on a hoist, in gear, and listen with a stethoscope.
Also, there is a tool you might be able to borrow or rent from an auto parts store that borrows them called the "Chassis Ear". It is a set of six microphones, a switch box, and headphones. You clip the microphones to suspect points, then drive around while listening with the headphones. You can move the microphones around to zero in on the source of the noise. Be aware that many mechanics have never seen or even heard of this tool. Suspension and alignment mechanics use it to find rattles, squeaks, and other noises.