If the vehicle has not been run or was missfiring you might have a partially plugged cat convertor which would "choke" out the engine operation (restricting air out which restricts the amount of air able to flow in) acting like a governor. That noise you here might be the insides of the covertor banging around in there as it gets hit and moved by the exhaust trying to find it's way through.

3=(PI.98 SWB 2.8TD-TH92.LWB 2.8TD)Red90 SWB.V6/bal,forged pistons,bore/95SR lkr&spr/2 bouncies/(ARB.w/Gorilla 12K winch/new stg gear/stg&sus/CJ side mirr/cust tow rec/01 SR wh w/Mich 265-70-16LTX/Rancho5000's/Candy Apple/rock crawlers/Hellas/KC's