Runs good cold and not hot could be Valve Clearances that are too tight.

Have you listened with a Mechanics Stethoscope around the Engine (or with what I like to use a 2-3 foot piece of wooden Broom handle) to localize where the sound is coming from?

Be sure to listen to the Vacuum Pump and the Timing Chain Tensioner.

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84 300D, 82 Volvo 244Gl Diesel