2003 Explorer, Assorted Problems

Ok, I have a 2003 explorer 4x4 xlt. Recently its started doing a few new things. First, in reverse, i sometimes get a loud clunking noise in the front end when I have the wheel cut sharply in either direction, more often to the left than the right though. 2nd, when driving down the road, there is a noise coming from the rear end thats like a humming noise that disappears when i let off the accelerator and seems to match road speed not engine speed. 3rd, the AC seems to only blow cold air out of the right center vent. It does not have rear AC. Lastly, when in 4wd, i'm once again getting the clunking noise while backing straight up and not turning. Anyone know anything about these problems?

I'd be suspicious of either CV shaft or transfer case for the clunks. Since you would have more tension on the front wheels than usual going backwards in 4x4 it could explain why the clunky is present while backing straight.

Rear end could be bad universal joint or steady bearing (not sure if the Ex has one or not) or rear end parts like pinion gear, pinion bearing, rear wheel bearings. Check for loose in the universals on the drive shaft first, then work from there. Check your fluids in the rear end and make sure they aren't low or deteriorated (milky consistancy).

Your AC sounds like you might have a blend door that either got dislocated, broken or has a bad control.