Anything besides diffs make a cracking sound?

[ICUBoy]

Thanks to all on this board who have inspired and problem-solved for me so much.
There was this noise from the front of my truck on hard starts and stops.
I have shimmed the front diff in my 3906 (emaxx with Feigao 8xl and mm) over and over (thanks to lincpimp and NitroRCracer elsewhere for the info). I thought I did a good job, with a nice smooth diff action when turned by hand and very litle play / no binding.
There is a persistent "crack" sound from the front of the truck and now I am starting to wonder if something else might be making the noise.
Any ideas anyone? Thanks very much.

[lincpimp]

When does it make the sound? While you are accelerating or braking? Can you make it do it when the wheels are off the ground?

My buddies bid the same thing. After putting my tranny in his truck we figure out it was the diffs.

[ICUBoy]

Thanks boys.
The sound is loudest and most consistent when braking heavily. It does happen at times at WOT but less loudly. If I pick it up off the groud it makes the noise when changing form forward to reverse (at speed- ouch!). I am contemplating new diffs but financially not a great time for the (beautiful but pricey) hybrid bulks and HB Lightning diffs. Thanks again fof the advice!