I have a slight knock (for lack of better description) coming from my rear end. It's a very pronounced knock directly proportional to drive shaft revolutions that increases with speed. You can only hear it when under load, speeding up or slowing down that is. If I'm coasting in between accelerating and decelerating it's quiet. You can really hear it when going below 20 miles per hour. Once you get up to higher speeds it's just a higher frequency and you don't notice it as much. I thought it was bad u joints (hoped) so today I jacked it up and put it in neutral to shake the drive shaft around and check the u joints only to find that the u joints are tight, and the play is where the drive train goes into the rear end. I can shake the drive shaft from side to side and it wiggles inside the rear end, I get a little less play when I wiggle it up and down. I didn't take the drive shaft out and check the pinion nut because I don't have any 12 point sockets or a torque wrench. I've never worked on a rear end, obviously, so I'm not exactly sure of the internal parts layout. I also put it in reverse with the wheels off of the ground to watch it and I held one wheel from spinning and that caused the sound to get much louder. Just wondering if I should bother buying some tools and checking the torque on the pinion nut or just take it somewhere. Obviously, if money wasn't an issue I wouldn't be on here asking questions..

a little history: I bought the truck 3 and a half years ago with about 90,000 miles on it. There was a wine coming from the rear end. Under the warranty that came with the truck I had the rear end rebuilt per the Ford service bulletin on that issue. (pinion not torqued properly at the factory causing gears to wear abnormally which caused a wine from the rear end.) The rear end was rebuilt per the service bulletin using oem parts, the issue was solved and I had no noise coming from the rear end for 3 years. Then a few months ago I start to notice this tickity tickity tickity sound when I'm going slow.

 

No one?

 

check the nut first. similar but more of a clunk from my buddys truck and the nut was just loose. but if not pinion bearing maybe?

 

Pull the fill plug and try to look at the oil. Or you could pull the cover off and inspect for damage.