I changed rear pads..slapped on ton of disc quiet..also added some in the the little spongey thing that the caliper goes through. I bent back all four dust shields. So far I haven't heard the noise.

 

I don't see a problem with the emergency brakes not working---- as long as they are not frozen or stuck in the 'on' position. I say that only when you have an automatic trans and put the SUV in park when stopped. The auto. trans pawl will hold it in place. Caution: if you have a manual transmission in your Blazer/Jimmy you do need good emergency brakes. Test your emergency brakes. Just because they 'click' when you depress the pedal and 'release' when you pull the black plastic T-bar, doesn't mean the E-brakes are holding your 4000 + lb. SUV. When those emergency/parking brakes are frozen on , your rear brake pads will be destroyed rapidly and your gas mileage will suffer. BTW the caliper pins can also cause this problem when they stick in the caliper. This is another common problem to look out for. In either case they may not make a noise until there is metal on metal friction. Then you need new rotors as well as new pads.

 

Thank you Jim for your expertise!! Mike, I didnt but I did change all vacuum lines, and poured some seafoam in vacuum system that same night. I do want to do the cable model, in steam of depending on vacuum for 4wd

 

The front diff can switch over from 2WD and 4WD. The change over mechanism is equipped with a proximity feedback sensor that detects the position of the mechanism. So, once You select 4WD it will keep blinking until the change is completed and vice versa[1].
In one position, the front diff is clutched in, the other one disengage the mechanism. My intention was to check if the noise You are experiencing is related to a front diff clutch mechanism.


[1] Although my firmware in '00 isn't accurate in this matter. I had a permanently engaged 4WD and it didn't indicate an error on 2WD, while it should. Les has a newer firmware and his one does.

 

Yup, that is a good idea. It happened to me several times already they got bent and spook me out. Somehow I didn't think of it while typing.