82 silverado 4x4 Drivetrain noise

[Dadda]

HI. My truck has developed a scraping/pinging/wierd noise when accelerating from 5 to 25mph. It seems like its rpm related, and mostly occurs in 1-2nd gear. If i drive just over idle speed in 1st gear its totally quiet, and over 30-35mph it seems quiet aswell.
 I can also hear it when i reverse slowly sometimes, its more like a silent scraping at reverse.

Rear wheel bearings has a little play but is still ok ! Front wheel bearings are 2k miles old. Cant be the flexplate cos there is no sound when its idleing, or if i just revv it in neutral.

I jacked it up and had my dad spin a rear wheel, I listened and only i could hear then was 2 ticking sounds at every time the drive shaft did a full lap. Sounded like it came from speedo cable area, or where my transfer case meets gearbox.

Setup 6.2D /Th400 /Np208/14Bolt And might be my spelling is somewhat off, im from Finland 

[Irish_Alley]

U joint. the ping can be the u joint click/bang and the aluminum drive shaft just echos the sound. replace both to be sure but it sounds like its the one near the transmission. does it do it more often when you go from reverse to forward or vice versa

silent scraping at reverse.

not to make fun of it but, WHAT.
dont worry about your English because im from the states and i still have problems with it lol

[Dadda]

It doesnt ping when switching from Drive to Reverse. Just the regular clunk from rear axle, yea it has some play  But the pinging/scraping sound starts after i start driving it. And its a bit irregular, comes and goes.
I greased the drive shaft U-joints today, i also checked the fluids and stuff. When i was standing on the front wheel, i rocked the car back and forth. And sure enough it developed som sounds. Well i will update if i find out whats causing it, but u joints or something wrong in the rear axle are the 2 areas i will start looking at.

And a very low scraping noise at reverse would sound better.  Not "silent"