This will be hard to narrow down.I did find a couple of TSBs on a noise like I think you are describing. Does this help?
This TSB applies to 2001 Explorer Sport/Sport Trac 4x4 vehicles, 1998-2001 Explorer/Mountaineer 4x4 vehicles (all build dates), and 2000-2001 Ranger 4x4 vehicles built after 11/1/1999 only.
Some 4x4 vehicles may exhibit a high-pitched "squeal" or "whistle" type noise from the front of the vehicle at speeds from 16 to 64 km/h (10 to 40 3 mph). This noise may be caused by the front halfshaft excluder (dust) seals (-3K070-) as they rotate against the inner front hubs. The noise may be more pronounced in cold weather conditions.
Install new front halfshaft excluder seals on each side of the vehicle. Refer to the following Service Procedure for details.
NOTE: THE METRIC HUB REMOVER ADAPTERS LISTED IN THE WORKSHOP MANUAL FOR THE INSTALLATION/REMOVAL PROCEDURES ARE INCORRECT. THE CORRECT TOOL NUMBERS ARE D93P-1175-A AND D93P-1175-B.
Perform the following for each side of the vehicle:
1. Perform the front halfshaft removal procedure per Section 205-04 of the appropriate model year Workshop Manual.
2. Restrain the halfshaft assembly by the outboard (wheel end) joint outer race. Clamp with a vise on the exposed metal surface only. The CV joint should be in an upright position (splined end up). Be careful not to damage the boot or boot clamp.
3. Remove the old seal by prying it off the shaft.
4. Clean the outer race of the CV joint of any remaining foreign matter.
5. Install the new Front Halfshaft Excluder Seal (YL2Z-3K070-AA) by pressing it onto the outer race of the outboard CV joint by hand or with an appropriate hand tool. All seal markings will be facing the bell of the joint (away from the stem).
NOTE: BE CAREFUL TO ONLY PRESS ON THE EXPOSED STEEL PORTION OF THE SEAL. START THE SEAL ON THE HALFSHAFT BY HAND, AND THEN PRESS ON THE EXPOSED STEEL PORTION OF THE SEAL IN 20 DEGREE INCREMENTS AROUND THE SEAL UNTIL IT IS FULLY SEATED AND PARALLEL TO THE CV JOINT FACE. BE CAREFUL TO AVOID DAMAGING THE RUBBER PORTION OF THE SEAL.
6. Spread an approximately 3mm (1/8") thick bead of High-Temperature Wheel Bearing Grease (E8TZ-19590-A) onto the new seal lips.
7. Clean the inner surface of the knuckle (-3K185-/-3K186-). This is the metal surface the seals will ride against.
8. Perform the halfshaft installation procedure per Section 205-04 of the appropriate Workshop Manual.
9. Verify that the noise is no longer present.
NOISE - "BUZZING" COMING FROM ACCELERATOR PEDAL - 4.0L OHV VEHICLES
VIBRATION - VIBRATION COMING FROM ACCELERATOR PEDAL - 4.0L OHV VEHICLES
Model(s): Ford: 1999-2000 Explorer
Bulletin No: 00-7-5
Date: April 3, 2000
Some vehicles equipped with a 4.0L OHV engine may exhibit a vibration or buzz at the accelerator pedal. This may be caused by engine vibration that is transmitted through the accelerator cable to the pedal.
Replace the accelerator cable. This cable is approximately 30 cm (12") longer and will require a different routing which should reduce the possibility of noise and vibration. Refer to the following SERVICE PROCEDURE for details.
Refer to the appropriate Workshop Manual Section 310-02 and the following text for replacement procedures.
1. Attach new Accelerator Cable (F87Z-9A758-KA) on the same plastic retaining clip used with the original cable.
2. Position the cable so that the clip is between the two (2) foam sleeves.
3. Use a tie wrap to loosely attach the cable to the wiring harness which is in the back of the engine compartment as shown in Fig. Fig. 1.
4. Verify that the condition is resolved.
Now are you sure it is coming from the engine and not the drive train?
Does it do it sitting idle and racing the engine?
If you are driving do you hear it then?
If you are driving and put it in neutral and race the engine, does it get worse or go away?
Did you look at all of the hoses etc for any vacuum leaks or cracked/split hoses?
Sunday, October 4th, 2009 AT 10:26 AM