ITBS are noisy, as well. I am told that a surprising amount of sound can come from the induction side of things. A decent airbox can help with that, or possibly just insulating the engine lid. (Yes, more weight where you don't want it--in the back.)
Tim has posted something that looks like the Tangerine Racing Phase 9 silencers, with a muffler on the end. (For a mid-engine'd setup, yet!) While I'm not sure that would not have
any impact on the power or torque levels, I would bet a shiny nickel that it is one of the best power/torque/decibel tradeoffs you can make. Chris knows his stuff, and has been helping cars get under dB limits for decades.
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--DD