If your vehicle is showing whining or howling noise from the rear of the car at certain speeds, here are the most likely causes and the parts you'll need to fix each one.
The wheel bearing allows the wheel to spin smoothly. When the internal rollers wear out or pit, they produce a continuous howling or humming noise that gets louder with vehicle speed and often changes pitch when shifting vehicle weight (like changing lanes).
Tires that have worn unevenly (cupping or feathering), often due to a lack of rotation or worn rear shocks, will create a rhythmic howling or roaring noise at speed that is frequently mistaken for a bad wheel bearing.
The rear differential requires clean gear oil to lubricate the ring and pinion gears. Low fluid from a leak, or severely degraded fluid, will cause the gears to whine, especially under acceleration or deceleration.
Worn carrier or pinion bearings inside the rear differential will cause a distinct whine at specific speeds. If the differential was recently serviced or re-geared, improper gear backlash or bearing preload setup is a highly likely culprit.
On rear-wheel or all-wheel drive vehicles with a two-piece driveshaft, the center support bearing can dry out and fail, causing a high-pitched whine or howl from underneath the center-rear of the vehicle.