So, besides the sound engine was relatively smooth? If so I'd vote for chain tensioner/s failure as that sounded very similar to my SC when one of the tensioners collapsed...
Think ball bearings in a coffee can, right?
Hope it's only this and there isn't any additional damage and you get away with only replacing the tensioners, ramps and maybe sprockets... (under 2k)
Keep us posted on what the mechanic discovers, fingers crossed for you
__________________
Former Test driver & Production Manager Singer Vehicle Design
2009 Cayenne GTS, '81 911SC RoW Targa (lot's of goodies), '86 535csi, '84 633 csi (turbo charged-sold)
, '68 912 Targa (sold)
, '69 911E (sold)
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