low rpm noise

[MIRELOS]

Volvo Penta on my catamaran both engine have been performing flawlessly for 11 years, on my way north from winter escape I started to hear a noise from my starboard engine/transmission; the noise occurs when I engage the transmission with the engine at idle or low rpm, once the rpms go to cruising speed it disappears, it is a clanking noise as if it was about to stop, the noise does not happen if the engine is not engaged to the transmission at any rpm. Initial check does not reveal anything amiss to the eye and touch.......the only thing I can suspect is an alignment problem. Engines are D-110i.
Any input is appreciated.
Thanks in advance

[capt jgw]

I'd suspect the damper plate that connects the transmission to the engine flywheel. Those do fail sometimes. The plate looks like the clutch plate on a stick shift car and serves some of the same function. Has metal or rubber/plastic springs that even out the pulses from the engine. When those go the trans shaft is no longer firmly attached to the engine and causes noise & vibration. At higher rpm the load & centrifugal force might stop the noise. If the springs are metal and break you get the pieces banging around in there. You check by pulling the bell housing off the engine, might have to pull the engine out to do that. Damper plate will be bolted to the flywheel with the trans input shaft splined into it.

[sailingharry]

I will agree with jgw. We had the exact same symptoms on our 98 Yanmar. Replaced it with a plate from PYI, it is a synthetic damper plate and seems to be much smoother. About an hour or two of work in the water for us, maybe different for you. I forget the price but maybe $100 or $200.

One thing that I learned when it was apart is that the issue is primarily aesthetic. It does not seem to be something that will catastrophically fail at some point. It appears to be a fail safe design.