White smoke is either Coolant (steam), unburned Fuel (fuel not atomized so it was in small enough particles to burn) or water in your fuel (steam again).

Late timing can cause white smoke but since the problem comes and goes this does not seem likely.

If it was mine I would try runing staight Diesel Fuel from a Station you know sells clean water free fuel; as a test.

Air, maybe.

Sticking Injector Nozzle Pintle; possible as it can be intermittant. Try cuting out one Injector at a time and see if the clacking sound goes away when youy do that to any of the Injectors.

__________________
84 300D, 82 Volvo 244Gl Diesel