Have a 2000 F 250 Super Duty 4wd diesel. There is a noise in the front end when in 4 wd. Plow with the truck. Seems to get worse as I use it. Gets louder when truck turns or goes in reverse. Sounds like a tinging noise or high pitched grinding

 

Do you have the noise if the hubs are unlocked?
Do you have the noise if the hubs are locked and the 4WD disengaged?
Have you checked the CV joints at the front wheels ?
Also ,check the u-joints for the front driveshaft.

 

No noise if hubs are unlocked. No noise until 4 wd is engaged. Just changed both front wheel bearings. Checked u-joints. Do not seem to be the problem. They are not loose. Noise may be coming from transfer case?

 

Unless you can definitely hear/feel the noise coming from under the seat , I would suspect you have a u-joint going bad.A dry u-joint will squeal and chatter before entering self destruct mode.