Bad tick/knock. Big Prob i think

[NHays]

Just pulled in the driveway after about a 30 mile trip out of town. Got out of truck walked to mailbox and left it running to cool down. I then notice a bad ticking sound. I can usually hear a light ticking noise from drivers door of truck, but it never alarmed me before. this tick/knock is alot louder, and not normal diesel noise. I got underneath and listened, and pinpointed it down to flywheel are. now i did replace clutch recently but i know thats not the problem. I also noticed a hint of engine oil on the bell housing bottom. I do notice that at around 2300 rpm (roughly) that there is a sort of heavy knocking (bottom end), but its not really heavy and its been there since I bought the truck in june. Also this is a twelve valve cummins. Down to brass tacks. I have heard of rear thrust bearing failure, the heavy rear end tick/light knock really has me concerned. This truck is sitting in my driveway, and I am going nowhere until I get an answer from you all. What do you suggest. This is my only vehicle. how easy is it to pull pan? Really Need help.