Just got my truck out of the shop on saturday, the oil pump had rubbed a whole in the transfer case and the rear seal on the transmission exploded all at once. Well luckily I bought it used from a good dealership with 118,000 miles and they took care of everything. Took it out to the beach as soon as I got it so that I could test it out. When going into 4-hi for the first time it made a loud clacking sound(best I can describe what I heard). Sounded like the transfercase had some trouble kicking in. Well I put it back in 2-hi and then back into 4-hi, no problems and drove fine. Put into 4-lo for a while with no problems. When I went back into 4-hi I noticed a low(in volume and pitch) thumping noise (about once every 10-15 seconds), but couldn't tell where it was coming from. I plan to call today and let them know I am coming back at the end of the week to drop it off. What do ya'll think?

2002 6.6L Duramax LB7