As this is an old thread, probably should have started a new one...but anyways....
Wondering if the whining you hear is from the transfer case. Guess you could remove the encoder motor when the transfer case is for sure in 2WD and rule out some type of electrical gremlin causing the encoder motor to be activated.
Could also remove the vacuum line from the actuator under the battery, plug the line. This will keep the front axle from engaging...unless there is something broken that is letting the gear move and engage.

Just early morning thoughts.