On mine I could hear the encoder motor trying to activate, kind of a clicking sound, but it was not switching from 2wd to 4wd. I was told when they do this you can bet tha's the problem. The tech said that was one of the worst types of setups and GM really screwed the pooch on most of their 4wd's from the early 90's on up. Somewhere in the late 90's GM (supposedly) fixed the problem but the newer style still is their weak point and proves GM just didn't really fix that wink link. He said the only way to test one of the e. mtrs is by replacing it with one that works. They are great when they work, and when they don't makes you want to drive the sob over a cliff....lol R&R on the older ones was't too bad a job if you have a lift, but these newer ones is a pita kind of job, but it's doable.