I have an '02 Tahoe Z21. Recently, I noticed a bit of noise when driving 65 or 70 down the highway. It turned out to be the front driveshaft clanking. The front U-Joint on that was worn, so I replaced that, which stopped the clanking. However, shouldn't the driveshaft not be turning when in 2 wheel drive? There is a motor, which I assume to be a shift motor, that you can hear turning when you shift from 2 to 4 and back to 2. Is this is the shift motor that is supposed to disengage the front driveshaft, but it's just slipping and not pulling the transfer case out of 4? Is there any way to test this without buying a new motor just to find it's not the problem? A mechanic told me that the transfer case stays engaged 24/7, but that seems bogus to me. It sound like a lot of wear and tear for a model vehicle that seems to spend more time on-road than off.