Strange noise

I have a 98 1500 5.7 with about 170,000 miles and i have a problem. I have an annoying noise coming from either the engine or right underneath the driver and passanger seats. It sounds like a ticking kind of like if you hold something up to a fan and that noise you get. I can only hear it when i am accelerating and i dont think it is an exhaust leak because when i rev the engine in neutral i cant hear it. If any one has any ideas what i should look for any help would be greatly appreciated

Thanks

May be time for a new set of u-joints.

Is this 4x4?

Yes it is 4x4

Yes it is 4x4

its possible that the transfercase is failing...