Hi all, ive got the an odd and unnerving sound coming from the front of transmission/back of engine. Its definitely rotational, and I wold describe it as a rotational grumble/whirring. I at first though it was a bad wheel bearings but after replacing that them it was still present. Checked driveline and everything looks good. Truck drives absolutely perfect but if I go up and down the road and let it warm up, as I slow down you can hear and feel the grumble. I really only hear it below 25 mph. If I go faster it goes away which I also find odd. It is not gear specific. Ive put it in manual 1 and 2 and you still hear it but there is no sound in reverse!? I took a video to capture the sound best I could.. Im curious if you guys had anything I should check out without pulling the trans. What really has me scratching my head is there's no other symptoms. No Torque Converter slip, no delayed or rough shifts, just this sound thats feels like impending doom 🙃
I am mechanically inclined so if its a torque converter or something I'll probably be dropping the trans in my driveway but figured it wise to ask some experts before fixing what may not be broken.
thanks guys!
** was able toaget the video uploaded below

 

When you say the driveline looks good, , did you rotate the driveshaft with the wheels off the ground and see if there was any grinding/roughness coming from the the U -Joints?

If there are a lot of miles on the vehicle and those parts are original, they could be the source of the noise.

Couldn't pull up recording, , but what we do sometimes is to remove the rear driveshaft and run only with the front axle and see if the noise is still present.
Could the noise be coming from the transfer case?

 

So I did what you said and jacked up the rear and ran it in drive last night. The sound could not be heard in the cab during that however when I had a buddy walk around the truck he could hear an odd rhythmic sound from the rear part of the truck socill probably go ahead and pull the rear drive line after work today and see if the noise is gone!

 

Hello, I replaced the rear u joint on the drive shaft.
Hit the freeway, and the u joint fell out, and drive shaft cracked at the joint. I had placed all the lock rings in, and everything seemed fine. As I drove off from the shop, it ran smooth. Vibration , was no longer in gas pedal. Got approx. 15 miles down road, , hit the freeway and all went bad, real quick.
I was lucky to have another , brand new u joint in truck, for the front joint, at transfer case, but was able to install it at the rear. The rear joint on shaft is cracked at the u joint cap, but, was able to manage the install with all rings in again. ( Won't last long!)
I limped at 3 mph, to a store, 6 miles away. Chirping sound is back...along with vibration, but damage at rear is extensive. I don't know what happened, during the dragging of the shaft for good 100 yards , before I could pull over, but when I got to the store, and got out, I noticed oil, under bottom of transfer case, or back of oil pan. It appears to be coming from directly below the transfer case which is covered by the frame? Nothing on sides, not from the seal, not from the tranny pan... Am stumped, and need my truck for work... And really need to work! The shaft I can replace...( After 3 pulls, I've got it!) But the new development of transfer case leakage has me stumped. There wasn't any serious noise involved in the dragging of the shaft...( All I heard was : " thump, thump thump, thump, thump" before I pulled over. And again, after replacing the u joint, the transfer case got me to the store, without any noise...or problems...
Thank you all. Appreciate your time.
1998 Ford f150 lariat, 4x4, 5.4L

 

You can drive the vehicle carefully in 4 WD , just remove the rear driveshaft.

Make sure there is sufficient lubricant in the transfer case,,,you don't want to run that thing dry.

Don't forget to ck the lube in the front differential.