what the he11 is this sound??

[ocbaud]

its a loud thumping/wood pecker sound that happens sometimes, mostly during coming to a stop. its under the truck and sounds like its coming from behind the cab. its a really fast thumping sound too. the driveshaft and ujoints look good and its not hitting on anything. everybolt on the rear end/susp. is nice and tight, the exhaust hanger IS a little loose, but it wouldnt be clattering around that much or as fast as it is. i checked the drums and all the hardware is in place and looks good.

if i had to describe it better, i would say it sounds like a rod knocking. but it only does it for maybe 1 second at the MOST and only when decellerating but not always. it started 2 nights ago.

the only thing that has changed on my truck is that i am using my friends valve covers with no baffles and i lashed my valves because some of them were loose(havent been adjusted since we started up the engine for break in).

i'm positive its not engine related, because the engine still has tons of power. taking it up to 6000rpm's it doesnt sound anything but great. at speeds of 100+ it doesnt make any weird noises either. just when coming to a stop.

i checked the caliper bolts and they are all tight too.