So yesterday I took a 300+ mile round trip drive with my truck and along the way it developed one hell of a humming noise coming from the driveline.
It seems to be worse at slower speeds and when slowing down or accelerating. Its consistent at speed. Driveability isnt affected at all, I was still able to drive 80+ mph without an issue.

A few weeks ago I got my tires rotated and after that I noticed a slight hum when slowing down to a stop but I thought it had something to do with the tires because I hadnt gotten them rotated in quite a while. Apparently thats related to the current issue and its gotten worse.

What could possibly be the cause?

'06 F150 XLT Supercab, 5.4, 9.75" limited slip rear, 4x4

 

Humming is typically caused by 1 or more of the 4 problems below:

1. Bad driveshaft spline/yoke components.
2. Worn or out-of-spec rearend gear teeth.
3. Incorrectly indexed driveshaft.
4. Worn transfer case gears.

Save some aggrivation and just replace the whole driveshaft. That's what I assume to be your problem, if you're not getting any whining from the rear-end.

 

Its hard to pinpoint exactly where the noise is coming from but it seems further back than the transfer case.

One of my mechanic friends seems to think its a bad pinion bearing and hopefully he can check it out today like he said he would.

Im hoping its nothing too major.

 

usually when driveline probs u get a vibration and be able to feel a little or alot in steering..

 

Still havent gotten a chance to get it checked out but it seems to be getting worse.
I dont like just throwing parts at it unless I know its gonna fix the issue. Driveshafts arent cheap.

 

drive at a speed where the vibration is, then put it in nuetral while still turning rpm. does it stop ? if so its probably drivetrian

 

If it's a hum it sounds more like a bearing on the way out if there is no vibration while driving the truck. Does the truck have a carrier bearing? When was the last time you checked the rear diff fluid level? How about the tranfer case and front diff? Is there more of a grinding/chatter/racheting type sound or is it more of a hum? If it sounds like a grinding/chatter/rachet type sound look at the IWE's on the front.

 

I havent tried putting it in neutral yet, might have to do that tomorrow.

It seems to do it at all speeds though, just louder at lower speeds.

Definately a hum/howl and not a grinding type noise and seems to be coming from the rear of the truck. No vibrations or driveability issues, just the noise.

Im not sure if these trucks have a carrier bearing or not.
The last time the fluid was checked was when it was changed 30k ago. Theres no leaks though.

 

the noise is still there when I put it in neutral going 65+ on the highway

 

Usually the in cab "humming" is caused by rear-end vibration. PJB4x4 mentioned it was coming from the "rear". A good tester in the back seat would be able to confirm with a "seat of the pants" response.

Does the noise get worse on a turn? If not, it's definitely not the front making the noise.

Based on what you have said I would suspect:

1. The low speed hum is being caused by your tires.
2. The high speed hum is being caused by either an incorrectly indexed driveshaft, a bad rear driveshaft joint, or bad gears in the rear end.

If you're comfortable with a wrench, drop the rear driveshaft and check for binding joints. Make sure to mark both yokes so that you can put it back in with the same index. If that checks out (it probably won't because you said the vibration is getting worse), you'll want to take it to a drivetrain shop and have them check for tolerances in the rear-end. They can also let you know if the driveshaft is not indexed correctly.

 

It doesnt seem to change on a turn.

The tires have been on the truck for about 41k and have never made noise before. Still plenty of tread left on them too.

I really dont have much time during the week to check it out and I feel that I wouldnt know if something actually was wrong.

I think Im going to make an appointment to get it checked out this week.

 

Did you find anything? My 2005 screw w/ 88,000 miles started doing it as well. Pulled the driveshaft and found the rear u-joint was pretty dry. Thought that this will be an easy fix. Still humming exactly the same. Going in next week to pull the pinion and replace bearings there. Hopefully that does the trick.

 

If it's not causing any vibration, it could be the wheel bearings.

 

I'd be willing to bet that it's coming from the tires. You indicated that you rotated them recently and that you had not previously done so.
That's my opinion.

 

The bearings in the rearend were shot so I had them all replaced and now theres no issue.

Its been fixed since September.