Gravel Rattling In A Can?

[721JSD]

Hello again!! Hope everyone had a nice Thanksgiving. I have another question about my truck. Again its a 2001 Chevy 2500 HD Ext Cab SB 4x4 LS w/ 8.1 and 6 speed manual trans and manual shift transfercase , 4:10 gears, 93,000 miles. Heres what is going on. When I drive down the road, it sounds like someone is hanging under the truck rattling a can full of gravel. Lets say while going up a hill the engine is turning 2000 RPM (it really doesn't matter at what RPM...the higher the RPM the louder) it makes a constant chirping/"squealing" noise. Going down hill it doesn't make the chirping/"squealing" noise if I'm coasting at the same RPM. However, the "rattling" noise is still there. If I put the transfercase in neutral and coast off of a hill the rattling noise is not there. What do you guys think it is? Transfercase?

 

Thanks for any information that is supplied.

[BrockwayMT]

Hold the transfercase shift lever against it's stop while driving. If the noise goes away it's the shift linkage for the transfercase. There are two foam washers that keep the ends of the link rod from rattling. If they dry out or fall off it makes a noise like that.