I have a 99 expedition 4x4. I am hearing and feeling a niose from under the truck ,just under the driver seat. the noise ocours mostlty when letting off the gas and just taking off. seems to go away once a steady speed is reached. sounds and feels similar to gears slipping past each other or a chain slipping on a sprocket,but not a grinding sound. I really dont think it is the tranny .
sounds more like from the transfer case. i originally thought u-joints ,so I replaced them , in both drive shafts,but it did not stop the problem.
The noise started right after I had to put a spare on with a bfg 265/75 16 with the rest of the tires and wheels being a 305/45/22. Could one diffrent tire size cause a problem or is it just a coincidence. ony one have ant thoughts on what it might be?....H

 

No ideas?

 

do you have a lift or level kit on this truck? my buddy's truck dose the same thing and its because of the leveling kit put just enuff pinch on drive shaft and we had to put a spacer on it to get rid of noise

 

No lift, no level kit. I do however have one rear tire(spare) that is a diffrent size from the other three.
I have 3 tires that are 305/45/22 and one rear that is 285/75/16. I had one of the tires that went bad and am going to get new tires soon. The noise started the very next day after I put the spare on. Could this cause the problem,and why would it....Hal

 

Yes, that's the problem, and if you keep driving with two different size rear tires you'll destroy the differential. That's a bit expen$ive to fix! What you're hearing is the differential SCREAMING about the abuse it's taking.

 

I have a 1995 F150 4x4. Had noticed a clanking when I shift (5 spd), but not everytime I shift. Thought - U joint. But checked and does not seem to be the problem. Also noticed a shaking - not real bad - until I get some speed up. around 50mph or so, the shaking stops. AND - there is a roaring sound that also stops when get speed up. Had oil changed and was told my 4x4 linkage was broken. I was recently hunting in Colorado and used the 4x4 often. Could it be that the linkage broke DURING the trip and I dont have it actually out of 4 high? I am traveling and running out of $. Want to try to fix this for myself if I can. I still have a long way to go to get home. I am a woman, and feel that I cant always trust mechanics - espcially when they know that I am traveling. I know this is a tough question to answer online - but - any suggestions? ( I am also pulling a horsetrailer and 2 horses.

 

Well The problem was the diffrent size tire. The problem started as soon as I put the spare on and quit as soon as I put on all same size tires....H