Onan Emerald Plus nhe running quiet

Long story short I had an older onan marquis in my rv. Ran very quiet until it didn't run and was cheaper to replace. I sourced a rebuilt emerald plus for very little dollars and replaced the marquis. Big mistake. The sound difference was night and day. I pulled out the emerald and was about to chalk it up to learning a lesson and started looking for a marquis. I noticed both seemed very similar in parts so tried to find why the emerald was so much quieter. Well the marquis has a black metal box which deadens the sound. Those box panels also fit on an emerald plus. They are insulated and really make the thing very quiet. So next time someone runs across a broken marquis with the black metal box save the metal panels. Depending on which source is correct it may have dropped the decibels by 6. SO somewhere between one quarter and half as loud by swapping a few panels.