grinding noise in 1999 suburban

My 1999 Suburban 2500 makes a grinding/groaning noise when making sharp turns, left or right, only when it has been driven for a while. It almost feels like its in 4 wheel drive, but is not. Any ideas? Thanks.

My 1999 Suburban 2500 makes a grinding/groaning noise when making sharp turns, left or right, only when it has been driven for a while. It almost feels like its in 4 wheel drive, but is not. Any ideas? Thanks.

Does the noise come while you're turning the wheel or with the wheel stationary in the turn? The only real way to tell if it's in 4 wheel or not is to jack all four wheels off the ground and run it. If the noise comes while you're turning the steering wheel it's most likely air in the system. My '99 does this occasionally and I've learned to live with it.