Noisy tranmission

[Rose1989]

I have a Volvo D1-30 engine with matching Volvo Sail drive. The engine had done 1310 hours when a ringing banging noise occurred at idle out of gear but vanished as throttle was opened.
Over the next ten hours the noise invaded all of the rev range to 1800 and by then I was able to be in port and have the service agent inspect.
The problem was diagnosed as a faulty flexible coupling between engine and gear box. Removal of the engine showed that the hard rubber in the coupling partly chewed.
The coupling was replaced after a long wait(8 days delivery Australia to New Zealand). The noise was still present but quieter at idle and vanished as soon as the engine put in gear.
20 running hours later the noise at idle is loud reappears around 1400 revs and then vanishes.
Has anyone any comment