Hello. I have a 2004 F150 5.4 FX4 with a 9.75 in rear end 3.73gears with 825000 miles and the last month or so at low speeds its like a pulsating grinding noise and at speeds 40mph or higher it turns into more of a light whistle. I originally thought it was the axel bearings because I had a seal leaking so I just went ahead and changed the bearings and seals but it was no fix. Still got the noise. I have been researching all the threads and lookin up videos o the different kinds of sounds and no ones sounds like mine. I have a friend who is a tech and did pin point the sound to my rear differential, he is saying my pinion bearing. I know there is a kit for all that so it's not a big deal I just don't want to keep having to get new differential fluid and spending money on things that are not getting the problem fixed. Any ideas on what it could be? I'm you g to try and upload the sound it makes within the next day or so and tomorrow I'm going to pull the diff cover and check my gears. I could use some input on this. Any help is appreciated. Thanks!

 

so you have serviced the diff already and still have the noise ?? did you add Friction Modifier ?

 

Yes I used friction modifier. My next step is the pinion bearings? Not sure. Ill post a video of the sounds within the next couple days.

 

Here's the sound coming from my truck. Just recorded it today. Thanks for all the input.


http://youtu.be/FX2GtuPZhoo