loud ping sound from shifting

Hi, I'm new to this (sorry if I'm doing this wrong) and am having a bit of a problem. I have a 1999 tacoma, 4 cyl., 2.4L, about 110,000 miles, and automatic. The problem is that sometime there is a loud ping sound when I shift into Reverse (and sometime drive). It doesn't happen every time (and pretty much stops when I try to look for the source, LoL) it seems to be coming from the underneath and near the front. I'm just praying its not the trannie (but is not lookin good). Any thoughts.
Thanks in advance.

 

Does it drive OK? If so, I am guessing it's slack in the driveline being taken up when the transmission shifts into reverse. There is always a little bit of slack between the transmission and the rear wheels, whether it's bearings or ring/pinion or elsewhere. Engaging reverse after going forward (or vice-versa) can cause this slack to be taken up abruptly, causing the sound you hear. The inconsistency of the sound also points to this. Not much you can do about it, it should not be (or become) a problem, just make sure the truck is completely stopped when changing into or out of reverse. Of course I could be wrong... others will chime in. And welcome to Tacoma World.

 

thanks for the welcome.
I haven't noticed any difference in driving, but I have noticed something else. I've noticed a different noise that sounds like its coming from the same general area. There is a kind of clanking noise (as if I'm dragging empty cans), it doesn't happen very often, and it occurs at a low speed (probably under 30 mph) and usually only after the truck has been sitting for a while. The sound goes on for maybe 20-30 seconds and then disappears. My truck is in good condition and this is probably the only major problem its ever had. I've entertained the idea that it might be 2 different issues, but the timing (the clanking came about a week after the ping started) and location of the sound tells me its probably more than coincidence.