I have a 2000 F150 Ext cab Lariat 4x4, and it has 140,000 miles. Well there is a humming noise that starts around 35mph and fades out at about 45mph anyone have any suggestions about that? My other problem is while im driving when i let off the accelerator i can hear/feel a slight clunk, and then when i get back on the accelerator it's an even more noticeable clunk. It seems that there is play somewhere in my drivetrain. My U-joints seem to be fine. Can anyone help me out, throw some ideas out here?

 

Hummings normal- the clunk is the shaft on the spline is dry. Pull the driveshaft and use teflon grease on the spline ..

 

I agree with JBREW but if that does not solve it check the universal joints. Mine was doing the same hum and it would snap and crackle when trying to power brake. New joints did the trick for me.

 

From the Ford TSB -

CLUNK OR BUMP WHEN STARTING FROM A STOP

FORD:
1997-2005 E-Series, F-150, F-Super Duty
ISSUE
Some 1997-2005 E-Series/F-150/F-Super Duty 4x2 vehicles may exhibit a driveline clunk or bump that occurs as the vehicle starts to move forward, following a stop. This condition may be caused by the slip yoke not sliding smoothly on the output shaft splines.
ACTION
Lubricate the slip yoke with Motorcraft PTFE Lubricant. Refer to the following Service Procedure.
SERVICE PROCEDURE

1. Verify the condition.
2. Remove the driveshaft per Workshop Manual Section 205-01. Be sure to index-mark the driveshaft during removal to maintain alignment during reinstallation.
3. Lubricate the slip yoke with 7-13 grams (0.25-0.46 oz.) of Motorcraft PTFE Lubricant.
4. Re-index and reinstall the driveshaft per Workshop Manual.
5. Verify the repair.
6. BTW - Jbrew says any teflon grease will do.

 

If you have deep pockets , you can do this , the humming isn't hurting anything though..

Drivetrain - Rear Differential Whine/Hum Noise
TSB 05-23-3

11/28/05

REAR AXLE NOISE REPAIR

FORD:
1997-2005 Expedition, F-150
2002-2005 Explorer
LINCOLN:
1998-2005 Navigator
2003-2005 Aviator
MERCURY:
2002-2005 Mountaineer
This article supersedes TSB 05-12-6 to update the Service Kit and Service Procedure information.

ISSUE
Some vehicles may exhibit an axle whine or hum during acceleration, deceleration and/or cruise.
ACTION
An axle repair kit has been developed which incorporates most parts required for a comprehensive axle repair. The kit should be used instead of installing a complete axle assembly to repair an axle whine/hum. Replace Ring and Pinion with Axle Kit and Components.


I have a list of the parts for the f150 , if you want to spend the money and do it yourself - I think thats crazy though.. It's over 1,500 to have it done..

I run amsoil and 12 ounces of friction modifier and I can't hardly here it..