Why Does My 4 Wheel Drive Whine (Humming Noise)

Hearing humming noises when you are driving can be cause for concern. There are a lot of reasons why your vehicle might be making these sounds so do not panic until you know the cause.

Try to discern exactly where the sound is coming from and when the sound is loudest.

Common Reasons You Might Hear a Humming Noise

Auto mechanic working in garage to find humming noise problem

Tires

If you have off-road tires on your Jeep and you are driving on a paved surface your hum may be caused by your tires. The off-road tires are not designed to be run on hard surfaces like paved roads and when you drive on these surfaces a hum may be the result.

Check your tires for how the wear pattern looks. If they are wearing out on the inside faster than the out then you likely have bad u-joints. Specifically, the lower ball joint.

If the wear is greater on the outside of the tire than the inside then it is likely your upper ball joint that is going bad. 

If your tires are not properly inflated they could be causing the humming you are hearing. Check your tire pressure to make sure they are all inflated to the same level.

If you have been driving in a muddy area you could have mud on your wheel. The mud would through your tires out of balance and could cause the sounds you are hearing.

Front Differential Gears

Your differential gears send powers to your wheels as needed. Your tires do not always have the same amount of pulling power. The differential gear normally supplies the tire that is easiest to rotate with additional speed and power. A locking differential splits the power equally between the tires.

One thing the differential gear has to have is a proper level of oil to surround it. When the oil level drops the oil that is surrounding the gear will be put under greater amounts of pressure and this causes it to heat up more than it can tolerate.

If you have been driving through water there is a possibility of water in your differential. As the water heats up it can create steam and humming sounds.

How to Check Your Differential Fluid Levels

Male Technician Checks Brake Fluid Level in Car

If you are hearing a whining or grinding noise from your differential then low oil could be the issue. 

Other signs that the oil level in the differential is inadequate are:

  • Burning smells
  • Whirring or whining sounds
  • Unusual vibrations when you are driving

Tools you will need

  • Jack or lift to raise the vehicle
  • A 3/8” ratchet

You need to lift the vehicle so you can access the differential. If you do this using jacks and crawl under the vehicle you should be sure to place the car on jack stands so it will be stable while you are under it.

If you are in a shop, you can lift the car safely and walk under it.

You need a 3/8” ratchet to loosen the plug. If oil comes out you can check it to make sure it is clean and viable. If oil does not come out stick your finger inside to see how much oil is in the differential

If you do not get any gear oil on your finger, go ahead and add some at this time. You pour the gear oil into the hole opened when you removed the plug. Pour in enough gear oil that oil leaks out of the hole before you replace the plug.

Pay close attention to the vehicle after doing this. If you continue to hear a whining noise you may need to change the differential oil or you may need to speak to a professional.

Bearings or U-Joints

Wheel Bearings

Your wheel bearings can cause you to hear a humming noise.

A simple check of these will require you to jack the vehicle up and put blocks under it to secure it. 

Take your hand and rock the tire back and forth. Place one hand on the top of the tire and one hand on the bottom of the tire. 

If you can rock the tire and you hear a clunking sound then you may have bad bearings or a bad u-joint.

The whining noises that you are hearing may be coming from your U-joints or your driveshaft. When your u-joint is wearing out the connection between it and your driveshaft or differential is not as secure. 

Change the bearings

You are going to need to buy a new hub assembly and install it. You cannot replace just the bearings on a 4-wheel drive.

U-Joint

Signs of u-joint problems

  • Excessive tire wear on the inside of the tire
  • Whining or clunking sounds while you are in motion
  • Noise increases when you mash on the accelerator or when you let off of the accelerator
  • You feel vibrations when you increase your speed.
  • Leaks from your transmission
  • The vehicle will not move forward or backward

Test your U-joint for wear

  • With your vehicle in park and running place your foot on the brake.
  • Shift the vehicle into reverse.
  • Listen for a clunking sound. You may also feel a knock or jerk.
Replacing The U-Joint

If the universal joint has gone bad it has to be replaced. The cost of the new parts is relatively low, but you may need a pro to do the work.

Replacing a universal joint requires a specialized tool called a u-joint press. The change over can sometimes be done without this tool but it is difficult and usually frustrating.

If you do not own a press you can often rent one from parts supply houses.

Things you will need

  • Transmission fluid
  • Pan to catch fluid when it drains from the transmission’
  • Set of end wrenches from 3/8 to 7/16
  • Large c-clamp or universal joint press
  • Hammer
  • Pry bar or large screwdriver
  • Small slotted screwdriver
  • Lock ring pliers
  • Needle nose pliers
  • Carjack
  1. Jack the vehicle up
  2. Check under the front wheels to prevent the vehicle from moving
  3. Take the driveshaft loose. There are two clamps on the differential end and you need to unbolt those two clamps.
  4. Slide the other end out of the transmission. You will lose some transmission fluid.
  5. Bring the driveshaft out from under the vehicle so you have room to work.
  6. Remove the lock rings holding the caps of the universal joint in place
  7. Remove the caps using the press or c-clamp
  8. Remove the old u-joint
  9. Place the new u-joint in position and hold it in place while you insert new caps
  10. Install the new lock rings that came with your u-joint

Frequently Asked Questions

Are U-Joints Expensive to Replace?

Universal joints are not very expensive to replace.

Can I Simply Grease My Bearings?

You can on a 2-wheel drive vehicle but not a four-wheel drive.

Is Differential Oil Brand Specific?

Yes, you need to check your owner’s manual and use only the recommended differential oil.

Final Thoughts

When you hear a humming the first thing you need to do is isolate where the sound is coming from. Once you know more about the location you can start to discern the possible cause. If you have any doubts see a mechanic for guidance.

Related Articles
1. How Fast Can You Drive In 4WD High
2. Why Does My 4-Wheel Drive Clunk?
3. How to Put a Jeep Wrangler in 4-Wheel Drive

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