i believe its the trans that howls in 4wd high
 

first heard it a few weeks ago after the wind storm hit us here in nj, my girlfriends grandmother has her fifty foot pine tree rip out of the ground in her front yard. since it was only thirty feet from the street i said hell ill drag this sucker to the road and cut it up there instead of dragging everything by hand. I figured 4wd high was good (i have no idea how heavy a pine tree this sized weighs) and i hooked the tow strap to the tree trunk and started to pull. first 4wd high was struggling but the real problem was this high pitch howling i was hearing, went about ten feet and the noise started to bother me, soi stopped and put the truck in 4low the noise stopped and the truck drug the tree with zero effort. So i didnt think much more of it till today, got a little dirty trying to take the dog swimming and needed 4wd, as soon as i started to hit the skinny pedal and the motor made the tires turn that dam howl came back! rocked the truck a few times and ever time the motor lugged from trying to spin all three tire the same howl came back. switched to 4low to get out and the noise went away?????? went back to 4high and sure enough the howl was back? regardless i got out but now i have this howl when using 4high and im really working the truck hard in 4high. Im thinking torque converter is slipping making the sound and4low multiplies the power enough to make it go away from the ease it now has to spin the tires? im gonna go tomorrow and climb a few hills and see if i can get the howl to start again in 4high

Your transmission doesn't care what the transfer case is doing, it just sends power as requested to the output shaft. The only thing that's different in 4WD is in the transfer case and front drivetrain. That's where I would start.

but why would it howl in 4high then go away in 4low? its making me think the tq is slipping from the stress in high and then in low because of the torque multiplication from the t-case the tq isnt under as much stress and the howl stops?

what can i check? my t-case i drained fluid back in September again, ill check today and make sure its full still. my front drive shaft is fine checked that last night washing the mud off the undercarriage. only thing with the front end is one of my "updated" ford dust seals at the axle tube ripped in half again, other than that everything is either replaced or in perfect condition

So what happens in 2 wd? If howls isn't present then, sounds like it isn't a tranny issue as Tom suggests.
Maybe some stress under heavy load on transfer case high gearing that maybe doesn't interfere in low? Not sure that gear oil would help to solve yet.
I guess always better to start in low range when not sure of load weight.
Easy for me to say now.

To test this out, put the truck in drive, hold the brake pedal to the floor, and apply power. You can apply 100% power to the transmission in 2WD to see if the problem occurs. Don't do it for too long or you'll overheat the transmission.

just finished detailing the truck from my mud romp yesterday, ill go do what you suggested Tom and post back

truck wouldnt pull the tree in 2wd, tires just spun. so as soon as i engaged 4high and eased into the throttle you could hear the howl, 4low and the noise went away

Your transfer case is the issue here, if it's only howling in 4 hi your transfer case is the culprit, you most likely over stressed the gears, any way has this howling ever happened before?

What type of truck is this? Year, make and model? Manual transfer case or auto? Please help us help you :)

all info is in my sig, and its an auto tcase. No never did anything abusive to the truck and the other day pulling the tree is the first time the truck ever made noise

Yes, your torque converter is slipping. If you put a new one in it will slip, too. That's how a torque converter works, by slipping. It is working as designed.

Are you certain the front output shaft is engaged in 4H?

the shift pattern is 4L-N-2-4H

If the linkage (I'm assuming floor shift here) is set too far one way, the transfer case may be between gears just enough to slip the dog-teeth on the collar.

If it's electric, you should rethink your life choices. :-innocent

I mean slipping as in its going bad like excessive slipping

I have a electric shift tcase, and it works flawlessly! Hubs not so much that's why I have Warn premiums on the truck now

when I posted originally I was on my phone (which does not display sigs)

2004 F350 ext cab short bed 5.4 4r100 esof system 133k over maintained miles