4wd grinding noise

[hump]

I sometimes get a grinding noise when I first engage 4WD and no traction to front wheels. If I stop or reverse it engages and works. This noise can't be good news. My truck is a 97 sierra extracab with the pushbutton 4WD switches. Usually takes a few seconds (8-10) to properly engage. Is the actuator the old style with expanding gas? I've done a few searches but can't tell. Also I read that alcohol is bad news in an additive because it binds water to fuel, but does it also harm the IP even if there is no water(solvent vs. lubricant?). A buddy of mine uses "super diesel" additive to boost cetain but it is alcohol based.

[diesel65]

GM specifies no fuel additives with alcohol.
The front actuator could be tired and not pushing out enough when you engage 4wd.
The gas style actuator is a metal round cylindrical can with what looks like one wire, GMs new actuator if your truck was converted has a plastic case with a 5 wire connector plugged in.

[hump]

Thanks William, I will crawl under & have a look when the snow stops, if ever! Any idea where the grind noise is coming from. please excuse my lack of knowledge, I'm mechanically challenged for the most part, interested just the same.

[HANK1948]

hump, if you have a old style actuator it will be a thermal actuator that is a 2 wire connector,thats why it takes 8 to 10 sec. because it trying to heat up the actuator and thats why GM went to a electronic one (positive engagement) also are you moving when you engage the 4 wheel drive?, you should be thats what GM says, also if you have the old actuator, the new (electronic one) actuator you have to order a new wiring harness(because its 5 wires now) and spice a wire into the transfer case harness good luck.