97 yukon 4wd. Jerks and makes noise like its

engaging 4wd at speed is not recommended as the syncro set up is for low speed operation only Using 4wd on hard surfaces especially with your tyres does not allow the wheels to slip and so you get torque wind up in the transmission. This prevents the gears from disengaging as there is excessive load on the teeth. To unload the wind up either drive on a grass/ gravel/ slippery surface or stop and allow the vehicle to run backwards. IT all amounts to driving technique and knowing when and where to engage 4wd. There are plenty of books /magazines that explain the damage that will be done to the vehicle running gear if run in 4wd for long periods on hard surface roads.

check the actuator vacuum/ wires for operation as it sounds like the actuation is not completing the movement properly for the front hubs.

Very Hard to say where a Clatter is coming from.
Do you have an Automatic or Manual Transmission?
Does it make a noise when you are turning and it stays in 4WD?

inspect for worn components from output of transfer case to front diff input. If everything is tight and solid from those two points, everything else points to being transfercase internals. Make sure your actuator isn't faulty causing a "4x4 to 2x4 shift on/off"

probably got a weak servo at the diff.

First change tranny fluid and filter. Check the tranny mounts and motor mounts. The GM's also have an automatic torque converter clutch circuit that can cause problems just like this.

Probably all related , all these systems are interrelated .One won't work without the other. Could have a problem with the TAC system - electronic throttle control . Your best bet , take it an have the computers checked for DTC'S - diagnostic trouble codes . Do you know anything about automotive electronic's ,serial data communication networks ?

thottle positioning sensor? if trans has overdrive could be a lock up piece, dont remember name of it. there is a lucas oil product that might help. if it is the overdrive.

Give a try by change your transmission/filters and Transfer case oil.

sound like shift valves sticking in valve body.