spitzair

Hello everyone,
Just moved to Terrace, BC yesterday and while moving here my truck started to make a howling sound in the driveline. It is most pronounced while the driveline is loaded up. Just before I bought it it was apparenty in for some warranty on the rear end, and I'm thinking they somehow put it together wrong, what do you guys think? I want to take it to the dealer here but wanted to know if I could do something about it myself. I checked the oil level in the rear diff and it was fine...
The other thing the truck did the other morning was when I started it it made a strange "PopFshhhhhhhhhhh" sound and the revs dropped and came back up, almost sounded like an exhaust brake coming on but I don't have one installed (yet), then, climbing a steep grade, I passed a VW Van and it blew a huge cloud of black smoke. Since then it ran fine just smokes a wee bit on start and sounds like it slightly misses on one cylinder when it first starts. Is this something to be concerned about? It still runs great otherwise and has good power and has no codes.
Any ideas or tips and suggestions are much appreciated. Thanks.