1997 chevy suburban makes a loud clunk when I push the button for lo or hi. The clunk only happens once and then goes away. I have not used the 4x4 option for about 10 years and I don't remember hearing a sound like that. Should I be worried?

 

Are you in neutral? In my 2000 it says to be in neutral when selecting lo. Not sure if your design is the same as mine. Mine is totally silent when it slips into 4x4. I used it this winter for a few days and cycled through all the options. Just brain storming.. a loose/sloopy chain in the transfer case might create a clunk when engaged. Have you checked your fluids in the transfer case and the front differential? They are super easy to service and the fluids are cheap (depending on what you use). Bad U joint? Clunks are often caused by worn or loose parts that have play in them. If it were mine I would put it on jack stands and see what doesn't feel right under there.