Help?! Weird Noise from Dead Stop

[dougger]

I have a 2000 Silverado, 67000 miles, 5.3 in it and I have this strange noise that comes from what sounds like the rear but it is actually coming from right about the middle of the truck. When I am at a stop light, stop sign or just stopped and then start to accelerate there is a sound, almost sounds like a dog bark for just a split second and you don't hear it again unless I stop and accelerate again. I can accelerate fast or slow, does not matter. Nothing feels like it is slipping, runs great other than this sound. Great power everything, just that dag gone "Bark" noise.
If you have any ideas, please let me know.
Thanks,
Dougger