If its a Ping sound, almost certainly a u-joint. But, if you have a slip joint in the shaft instead of where it exits the tranny, then it might be worn.
Most common thing with it, is to come to a stop, and hear a loud clunk just when you release the brakes, usually even before you get on the gas.
On my old Ford, it got to the point where it felt like I got rear-ended every time I let off the brakes from a hard stop.
The splines wear in one place to the point where there is a slight offset. When you come to a stop, the joint cannot slip due to that offset. The suspension tries to move forward slightly but the shaft does not slip.
When you take your foot off the brake, it lets the splines rotate slightly and they line up again.
Then the shaft slips in suddenly and all the pressure is released.
Greasing the slip yoke will often stop the noise for a little while.
Internal slip yokes could do that too, but they run in oil and I have never seen one do it.
