Slack in the drive line.??
 

I have an 03 cummins 6speed and when i let off the clutch from a dead stop there is a whining/grinding like noise then if i hit the throttle it goes away. At highway speeds if you let off then give it more throttle it jerks a little.?. Checked the u joints all good should i look towards the rear axle? Tranny tailshaft??

Sounds like the clutch is going out on you. Does it make the noise when parked, idling, with trans in neutral and not pushing on the clutch?

Not the clutch. No noise when idling. Ended up being the rack and pinion. Replaced it everythimgs all good now thanks anyways bud