When my truck is in 4 HI and I accelarate and decelarate the transfer case makes noise, but not while just cruising?
My truck is a 1990 GMC long bed 305 5 speed 4x4 w' 10,000 miles on it.

well, since no else has said it yet... '90 w/ only 10k miles; it aint likely broke in yet! Have you checked fluids; changed fluid?

I haven't yet "shame on me", but the truck did sit for an extended period of time, the undercarrage shows it, it was parked on top of grass.

be more specific, what type of noise? grinding? whining? after sitting for that long and being 15 years old, you should definitely drain all the fluids (tcase, tranny, differentials, etc.) and replace with new fluid.

Kind of like a grinding noise, like rahrahrahrah, as your accelarating, and the noise becomes more noticeable as you shift into the higher gears and the speed picks up.

first step for a grinding noise is lubrication, have you inspected and changed the fluid?