I have a 1996 chevy blazer and dont know how to disengage from four wheel drive to two wheel drive?

it will bolt up but your problem is all the electronics and sensors dont match up

That, I believe, goes to the popular but ever elusive chevy accumulator. Its mounted behind the inside right fender, behind all the other clutter. You really have to know where and what to look for. Please search on "chevy blazer accumulator vacuum hose" and take your pick of any the gadzillion pics/videos.

shift it to 2 wheel drive run it in reverse short ways

driving in 4wd on hard surfaces produces what is known as torque wind up as the wheels cannot slip so the variations of distance going around corners , dips in the road etc place considerable strain on the transmission , transfer case , drive lines and diffs
that is why it is difficult to get out of 4wd unless you drive with 2 wheels on a grass verge to relieve that torque wind up
as for the noise check wheel bearings and the cv ("U") joint at that wheel as there appears a proble where the dog teeth in the hub are not engaging properly or are jumping out of engagement

I'm thinking you might have unplugged the switch for the 4 wheel drive switch mounted on the surround for the stereo, when you installed the CD player, or maybe broke something asscociated with that switch.

It has been a long time since I drove one of those. I believe there is a stick in the floor for engageing and disengagine the 4wd.

remove the shaft from transfer case

sounds like either a fuse or the do u have locking hubs that need to be engaged also when using 4 wheel drive there is actually only 2 wheels turning usually passenger front and driver back sometimes u also have to drive backwards to engage and also disengage 4 wheel drive finally it may be a transfer case problem check drive shafts and u joints make sure they are engaged

WI replace the wheel bearing and put brakepads on.This is when the problem start...When I am driving I hear a stumping and humming sound. 1996 CHEVELETE BLAZER . YOU CAN PUT IT IN FOUR WHEEL DRIVE

its the actuator on the front diff . this is a common problem and a easy but expensive fix