Sound coming from right side.
 

I have a 2000 Lt 4x4 blazer auto with 93,350 miles on it.

When I do a med to fast start (from a dead stop or kick it into passing gear) I hear this whistleing sound coming from what it appears to be behind the pass side kick panel.

From what I can gather from reading other posts, that should be where a part of the 4x4 engagement is. (my 4x4 is acting up also, just blinks when I put it in auto, 4 lo or 4hi).

Is there a vacuum hose behind that kick panel?

There is a actuator under the battery that has a vacum line running to it that pulls it into 4 wheel drive .I would remove the battery and see if the vac line has a hole in it and see if actuator has vacum to it and if actuator moves when you put it into 4 wheel drive