My 2003 EXT Trailblazer has 70 K miles and when I put the transmission into AWD it has started making a strange noise. It sounds like friction is created, like a couple of metal plates are rubbing together. The sound goes away when I put it into 2 wheel drive. Any idea what might be going on and how much it might be to fix? Thanks in advance.

Welcome to AF. Better have this checked sounds like a transfer case issue.

Hard to say without some troubleshooting. A4wd, livens up the front axle, causing the entire front drivetrain to rotate right up to the transfer case output. The clutch in the transfercase will then engine/disengage the ouput as triggered by rear wheel spin. It's not a true "AWD" system. At 70Kmi you are due for frt, rear diff and transfer case fluid changes at a minimum.

Joel