Triumph Repair: Rear wheel noise, scrape marks, steep driveway

Question
Follow up to answer of 6/28 2010. The noise is a knock, not a crunch or a scrape or a whine. From inside the car it sounds like its behind the seats ie near the diff. We do not think its related to one wheel having listened to it many times. With the car on stands and wheels off we jacked up the axle to vary the angle of the shafts with the wheels turning under power. No knock in any position. Extensive looks underneath show no knock or scrape marks. The U/Js seem free on rotation but no play when inserting a screwdriver between the joints. No amount of rotating or rocking the wheels will produce the noise.  One clue. We have a very steep driveway about 80 yards uphill and going up, with the car leaning back on the rear spring the knock does not seem to happen. Once at the top it returns, straight, right hand circles and left hand circles and going back down the driveway with the engine off its there at any speed. Cant go any further as the car is not yet licensed for the road. Still baffled as I do not know which section to dismantle.  We did take off the drum, new shoes everything fine. We also swapped the wheels.
Roger

Answer
When going up the steep grade, the only difference is a high load on the whole drive train and the spring is compressed and all slack it removed from most everything. You might try moving the car on level ground with the hand brake on hard to duplicate the load part. This would not load the rear spring but would load all drive components to see if the noise changes any. Then have a couple of friends sit on the trunk and move the car on level ground with no brake to duplicate a compressed rear spring to try to isolate the noise further.
Howard