I have a 97 chevy s10 LS 4x4 with the 4.3l. My 4x4 went out in the truck as it made a very loud grinding/rattling noise. As I'm driving in 2wd it still makes the same noise, but sometimes stops after I've been driving for so long. I don't know if it is the transfercase, front diff, or something else. Anybody who has an idea can help please!

SOURCE: 2004 F150: When in 2wd the front end makes a noise like a rat...

I had this problem too. It could be a few different things but all the same result, loss of vacuum causing the 4wd to start to engage but not completely. The teeth on the clutch in the locking hub are grinding on the spline of the cv shaft as you lose vacuum and it tries to go into 4wd which is the default if everything would fail. 1st thing could be either of the 4wd locking hubs (approx $200 ea., located on the back side of each front spindle), check them to make sure the vacuum lines on the top of it are still attached these require the brakes, tie rod and upper ball joint to be removed if replacing, 2nd is the 4wd vacuum actuator (approx. $40 located on the firewall passenger side behind the battery) Ford has replaced this part with a modified one that has a little roof on it to stop the water that drips of the hood when it rains and makes it short out, this is very easy to replace (2 nuts) and last if both the above are working just fine would be to trace all the vacuum lines for a break unfortunately it is a 6-8 foot line for all the front 4wd and it costs approx. $100 if you have to replace. Not very difficult just time consuming. Hope some or all of this helps.