OK folks, I need some help.
95 T-100 with 238K miles. I have a pretty loud whine that begins around 50mph and gets louder at higher speeds. It stops immediately when I let off accelerator and is completely silent when coasting.
I've replaced hanger bearing, all u-joints have been repeatedly checked etc.
The only thing I can think of is about a year ago, the rear differential got pretty low on oil and I've been thinking that the front pinion bearing might be bad.
I pulled the axles and 3rd member and can't find anything that shows wear although pinion bearing does show a little bit of discoloration.
Everything feels tight and looks good otherwise.
Any ideas before I just give up and bolt it back together till something fails?

 

I am having the same issue with the truck i just bought yesterday. Did you ever figure out exactly what was causing it.