79 300 SD klacking

My friend has a 79 300 SD. He has a loud clacking sound as distinguished from the normal klata klata.
The car runs fine starts easily and suspecting injectors he replaced them
with no change.
He says that the noise tends to be worse if the oil level is high rather than low.
He also reports that the noise does not seem to be coming from under the valve cover.
Any ideas of what the cause of this noise might be?
--
Roger Shoaf
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Three ideas:
Air cleaner support bracket is broken at its rear leg.
Timing chain is slack; tensioner s/b checked.
Vacuum pump (on front of motor) is disintegrating - dangerous as parts can fall into timing chain sprockets killing the motor.
More information is needed for meaningful suggestions.
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What more information do you need?
--
Roger Shoaf
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How many miles on the motor? When were the valves last adjusted? Did this noise suddenly occur or did it come on gradually? Is the noise present on cold start as well as hot idle? What SAE weight oil is in the motor? What's been done other than new injectors? Any investigation of the drive belts, pulleys, alternator etc.?
--

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says...

When my 617 started going clackety clack instead of tapa tapa, it was bearings.
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