Mechanical reasons:
* Worn bearings: Over time, the bearings in the transmission wear out, causing a humming noise when the transmission operates.
*Worn Gears: Worn gears can also make a humming noise, especially when changing gears or driving uphill.
*Low Transmission Fluid Levels: Low fluid levels can starve transmission components of lubrication, causing a humming noise.
*Dirty or contaminated transmission fluid: Contaminated fluid may contain particles that can damage transmission components and cause a humming noise.
* Loose bolts and fasteners: Loose bolts and fasteners can cause vibrations, which can lead to noise.
Electrical reasons:
*Faulty Input Shaft Speed Sensor: A faulty sensor can send incorrect signals to the transmission control module (TCM), resulting in incorrect gear shifts and a humming noise.
* Faulty Shift Solenoid: A faulty solenoid may not operate properly, resulting in delayed shifting and noise.
* Faulty electrical connectors: Faulty connectors can disrupt electrical connections, causing shifting problems and humming noises.
Other reasons:
*Worn torque converter: A worn torque converter can create a droning noise, especially when accelerating.
*Damaged Differential: A damaged differential can cause a humming sound when driving in a straight line or when turning corners.
* Incorrect transmission control system pressure: Incorrect pressure can cause shifting problems and noise.