The Humming noise is NORMAL, but for those who want to fix it there is a TSB Ford initiated on it -

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.
NOTE REFER TO THE "DIFFERENTIAL RING AND PINION" IN-VEHICLE REPAIR PROCEDURE IN THE ONLINE WORKSHOP MANUAL SECTION 205-00, FOR THE LATEST AXLE DIAGNOSIS AND REPAIR PROCEDURES.
NOTE FOR 1999 AND PRIOR MODEL YEAR VEHICLES, USE THE 2000 MODEL YEAR WORKSHOP MANUAL.
NOTE WHEN SERVICING THE REAR AXLE ON ANY 2002-2004 F-150, EXPEDITION, NAVIGATOR, EXPLORER OR MOUNTAINEER BUILT BEFORE 3/30/2004, IF FLUID REPLACEMENT IS REQUIRED, REPLACE THE ORIGINAL FUEL EFFICIENT HIGH PERFORMANCE (FEHP) SAE 75W-90 REAR AXLE LUBRICANT WITH SAE 75W-140 HIGH PERFORMANCE SYNTHETIC REAR AXLE LUBRICANT. WHEN THE FLUID TYPE IS CHANGED, REPLACE THE CURRENT "FEHP" METAL TAG WITH A NEW "75W-140" TAG (F3TZ-4121-AA). IN ADDITION, REMOVE OR BLOCK-OUT THE FEHP REFERENCE ON THE MULTI-COLORED LABEL LOCATED ON THE RIGHT SIDE AXLE TUBE. IF THE AXLE IS A LIMITED-SLIP MODEL, USE XL3 ADDITIVE FRICTION MODIFIER IN THE QUANTITY RECOMMENDED BY THE WORKSHOP MANUAL.
KIT ORDERING: REFER TO THE VEHICLE AXLE
TAG FOR AXLE RATIO IDENTIFICATION
^ 5L3Z-4209-A = (8.8-Inch Ring Gear/3.31 ratio)
(1997-2005 F-150)
^ 5L3Z-4209-B = (8.8-Inch Ring Gear/3.55 ratio)
(1997-2005 F-150, 2002-2005
Explorer/Mountaineer/Aviator)
^ 5L3Z-4209-C = (8.8-Inch Ring Gear/3.73 ratio)
(1997-2005 F-150, 2002-2005
Explorer/Mountaineer/Aviator, 2003-2004
Expedition/Navigator)
^ 5L3Z-4209-D = (9.75-Inch Ring Gear/3.31 ratio)
(1997-2005 F-150, 2005 Expedition/Navigator, 1997-2002
Expedition/Navigator)
^ 5L3Z-4209-E = (9.75-Inch Ring Gear/3.55 ratio)
(1997-2005 F-150, 1997-2002 Expedition/Navigator)
^ 5L3Z-4209-F = (9.75-Inch Ring Gear/3.73 ratio)
(1997-2005 F-150, 1997-2005
Expedition/Navigator)
NOTE 9.75 REAR AXLE HOUSINGS WERE REDESIGNED IN MID-1999, INCREASING FRONT PINION BEARING SIZE. REPLACING RING & PINIONS IN AN OLD-STYLE AXLE ASSEMBLY WILL REQUIRE INSTALLATION OF SPACER P/N YL3Z4662-CA. SPACER IS TO BE INSTALLED BETWEEN INNER PINION BEARING AND COLLAPSIBLE SPACER.
THE AXLE SERVICE KITS INCLUDE THE FOLLOWING COMPONENTS:

^ 4630 - Head Bearing
^ 4628 - Head Bearing Cup
^ 4676 - Pinion Seal
^ 386989-S2 - Washer (Slinger)
^ 4621 - Tail Bearing
^ 4616 - Tail Bearing Cup
^ 4222 - Differential Bearing Cups
^ 4221 - Differential Bearings
^ 4209 - Gear Set (includes pinion shims, pinion nut and crush spacer)
^ 4209 - Instruction Sheet
NOTE THE KIT DOES NOT INCLUDE THE FOLLOWING ITEMS. SOME OR ALL OF THESE ITEMS WILL BE REQUIRED TO COMPLETE THE AXLE SERVICE, DEPENDING ON AXLE APPLICATION/STYLE.
ORDER AS NEEDED:

 

NOTE REUSE OF RING GEAR BOLTS, CARRIER BEARING CAP BOLTS AND DIFFERENTIAL SLAVE PIN RETAINING BOLT REQUIRES CLEANING OF THREADS AND INSTALLATION OF TA-27 STUD AND BEARING MOUNT RETAINING COMPOUND & SEALANT.
^ YL3Z-4662-CA - Pinion Bearing Spacer for
1997-1998 9.75 axles
^ XG-14 - Gear Marking Compound
^ 4067 - Differential Shims 0.241" to 0.307"
^ SAE XY-75W140-QL - High Performance Synthetic Rear Axle Lubricant
^ XL-3 - Additive Friction Modifier (Limited Slip Axles Only)
^ 205-506 - Seal Protectors (Rotunda Tool)
^ W710084-5439 - Wheel End Nuts
^ 390266-S199 - Differential Slave Pin Bolt (9.75" axles)
^ 387426-S100 - Differential Slave Pin Bolt (8.8" axles)
^ 4B422 - Axle Circlips
^ ZC-21 - Metal Surface Cleaner
^ TA-29 - Ultra Silicone Sealant
^ TA-27 - Stud and Bearing Mount Retaining Compound and Sealer
^ F3TZ-4121-AA - Fluid Tag (REQUIRED IF FLUID TYPE IS CHANGED FROM FEHP DURING REPAIR)
WARRANTY STATUS: Eligible Under Provisions Of New Vehicle Limited Warranty Coverage

OPERATION DESCRIPTION TIME

052303A 1997-2002 Expedition, 4.7 Hrs.
1998-2002 Navigator,
1997-2004 F-150 Heritage,
2004-2005 F-150: Rear
Axle Noise Repair
(Includes Time For Road
Test To Verify Concern
(Beam Axle)) (Do Not Use
With 4205A Or 4205A4)

052303A 2003-2005 Expedition: 5.8 Hrs.
Rear Axle Noise Repair
(Includes Time For Road
Test To Verify Concern (lrs
Axle)) (Do Not Use With
4010D Or 4010D4)

052303A 2003-2005 5.9 Hrs.
Expedition/Navigator With
Air Suspension: Rear Axle
Noise Repair (Includes
Time For Road Test To
Verify Concern (lrs Axle))
(Do Not Use With 4010D
Or 4010D4)

052303A 2002-2005 6.6 Hrs.
Explorer/Mountaineer,
2003-2005 Aviator: Rear
Axle Noise Repair
(Includes Time For Road
Test To Verify Concern (lrs
Axle)) (Do Not Use With
4010D Or 4010D4)
DEALER CODINGCONDITION
BASIC PART NO. CODE
4209 14
OASIS CODES: 509000, 590000, 597997, 702000, 702200, 703200, 703300, 703400, 790000

Whewwyy, that was ALAWT of typing!!!! Hahaaa ( : - .....

 

I've got a 2005 ext cab flareside xlt. 5.4 liter 4x4 3.73 LS. I'm getting the whine noise. Truck has like92k miles on it. Its noticibly louder as I come to a stop. otherwise it sounds like tires...I thought it was, until I realized that the noise was the same on dirt roads or pavement, no matter bumps or speed...I'm gonna go by the dealer and see if any of these TSBs that I keep reading about pertain, and if not, then I may tackle it myself...or trade it in! LOL! I just spent a bunch of $$$ for a spark plugs and a catalytic converter...I'm not enthused about dropping another 12 hundred bucks on this truck, when I need tires, and and an exhaust manifold or gasket too!