I have a 1999 Chevrolet Silverado 2500 non hd 4x4 with a 6.0 in it, during this winter i started to notice this loud ticking/cracking noise coming from front passenger side up under the truck, my dad a 25 year mechanic said he thought it was a cracked flywheel, so we paid $400 and replaced the flywheel, the old flywheel had a little crack in it so we figured had been fixed. Well driving it home from the shop i start to here the noise again. It started off not bad, but then went back to its normal sound. If anyone can please help out me out on this one it would be greatly appreciated, cause this noise is so annoying.

Special notes
I had a leveling kit put on about a month or two before this started happening.
The truck will only make the noise under a heavy load as if your just starting off.
The truck will not make the noise in neutral if you give it gas.
My dad is also pretty sure its nothing in the motor, cause you cant hear it in the engine bay.