well after more miles and a lot more looking, i have narrowed down the sound being generated. after extended highway drives (30 min or more) there seems to be a gear whine that develops that is more noticeable in 4th and 5th gear. after this noise begins, so does the low speed turning clunk. clunk only occurs when the car is out of gear and coasting such as into a parking spot or my driveway. once it cools down, sound vanishes. i opened up the rear end and found that the gear wear pattern looks perfect and the gear lash in perfectly within spec. the only oddity i notice is that there seems to be a lot of slack from the point of turning the driveshaft till the wheels catch up the slack.
any help would be great.