Rythmic Loud Bang Clank Clang Coming from fan engine transmission area

Loss of power uphills and in general. Steady loud noise. Engine dies even on slight hill, very low power. Remains on in neutral, but noise is persistent almost always while running. Louder on the right side of the vehicle when standing in rear. Loudest while sitting in vehicle coming from behind. Cooling fans spins smoothly, I so do not think its that. Sounds like possibly metal on metal. Occasionally the noise lessens while changing gear into reverse but power loss stays the same. Started while going up a big hill and began loosing power, got progressively worse and louder. The rhythm of the clang is almost always consistent. No grinding. Nothing is visually wrong. It can be felt through the floor of the car under your feet. Its a Dune Buggy/ Sand-rail
that has been running smoothly until this noise began.