The belt tensioner damper can make a lot of noise. Mine sounds like there are marbles in the engine. Put pressure on the upper attachment of the damper and/or pry it away from the head. Don't slip and hit the fan! If the noise quiets, you need a new damper. MB brand dampers cost more but last a lot longer than other brands.

Is the smoke consistent or does it clear as the engine warms? It might be a lazy glow plug. If it smokes all the time, I'd check IP timing and run a can or two of Lubro Moly Diesel Purge directly, not diluted in the fuel tank, to see if that helps. There's also an Italian tune-up. If possible to do safely and without risk to your license, run with the fast crowd in the left lane in third gear for a few miles. Mind the engine temperature gauge. Hopefully the smoke will clear in a couple of miles. Otherwise they'll impound your car, put you in jail and make you drive an electric car

Other sources of oil into the combustion chambers are worn valve stem seals or guides, worn turbo seals, excessive blowby, etc. which require extensive engine work, but don't typically cause more engine noise.

Sixto
87 300D