End play like you describe is normal for that style of rear end. Look carefully to see if you have a cracked leaf in there somewhere making the sound. The rear end itself shouldnt be capable of creaking.If you added leafs without any anti-squeeking shims (plastic) between them it may be the source of the noise as well.Check the eye bushings and shackles too to be sure they are tight and good, even try unhooking the shocks from the rear end to see if the noise goes away, one may be bent