Most commonly this is a tire wear issue
bad wheel bearings will do that, usually in the front.
Check the bearings.
it would most likely be the bearings but in some cases sometimes the axle make a humming noise when traveling at high speeds.(front wheel drive)
It could be the bearings on your front driver side wheel.
id say type and size of tire, and if bearings are bad either or will make that humming sound.
is the humming coming from the front end of the vehicle? i have a 1996 explorer with the same issue. yes the noise come from the front but not all the time seems to make the humming noise when it gets hot
Worn passenger side front wheel bearings.
i would first balence the tires then try replacing the wheel bearings if the noise is coming from a specific area on the car In example left front, right front etc.
could be your wheel bearings
1999 Mercury front and humming noises can because by several things. Tire noises are the most common cause. A tire that is not wearing properly can cause a humming noise.
A humming noise on a 1999 Park Avenue is caused by bad wheel bearings. When bearings are loose or worn they will create a loud humming noise that will get louder and louder as the car accelerates.
when the pump is going out it will make a humming noise from the bearings even if the resivore is full.