I run my boat on Tahoe in the summer and probably right at the sound limit. If i needed a quick fix to muffle the exhaust, is there any tricks. Maybe an insert or slip-in since there isn't anything to clamp onto the outside. I have the typical HEAT stainless 4 1/2" (?) exhaust that is flush mounted on each corner of the transom. TIA.

Look into ggb inserts. Work well and don't rob power.

They look ideal. But GGB isn't selling them right now - apparently the other products lines are doing well.