Buzzing could be faulty pre-glow relay? No glow plugs glowing, no engine starting? Do you smell raw diesel fuel in the exhaust while cranking? You could also crack open one of the injection hard lines to see if fuel weeps out while cranking.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC