Crunch sound from rear of truck
 

F-150 2003 5.4L Triton V8
I replaced my rotors, e brakes and currents are in good shape but there is still a crunch sound I stop and go, change gears and the truck kind of rocks unless I put in e brake before letting go brake.
Any thoughts? Video link is below for reference.

If you jump on the bumper do you still get the noise?

No it doesn't

Any play in your driveshaft

What do you mean play? I know my drive shaft is leaking and I haven't replaced the gasket yet.

I meant that if you put on your parking brake with your trans in neutral and grab your drive shaft and try to move it it shouldnt very much at all. Can you get a pic of the leak? Drive shafts dont leak.

Crunch sound from rear of truck
 

Is it leaking from the transmission or the rear end?

It's leaking from the rear end opposite side of the cap of the differential. I'll have a pic up shortly

Crunch sound from rear of truck
 

Rear pinion seal, just had mine replaced a couple months ago. But I had other work done so I don't know exactly how much it would cost you to have just that replaced.