No start 1982 300SD diesel on 1992 Mercedes-Benz 300SD

Prior to no start, engine wouldcrank weakly, as if battery was dying but would start right up with jump. Battery is charged. After no start, cleaned terminals and cable ends of corrosion. After tightening ends to terminals, now car makes loud buzzing (not clicking) noise as soon as I turn key, before cranking.

Diesel engines have very high compression and need a very strong battery to start, as well as a good starter and battery cables. Have these all checked out thoroughly.