I went to 1 ton running gear with a D70 in the rear. I have been running the stock driveshaft with no problems. I just replaced it with a 1 ton shaft out of a CUCV I had shortened, balanced, and new spicer u-joints. I also put a 1350 yoke on the D70. It's an 1981 Blazer, np208, 4" in. blocks in rear. Now when I drove it I have a noise that doesn't sound good. It's only when I let off the gas I hear a metal vibration sound. I don't really feel anything I just hear it. If I get back on the gas it seems to go away until I coast again. When I came home and looked under it everything seems fine. The u-joints aren't binding and full of grease and pulling on the driveshaft it's all tight, no leaks from the 208 or D70. I'm going to check the fluid in the D70 and 208 next and put more grease in the u-joints. Anyone have any ideas??? Thanks.