*Update*

I was reworking the exhaust ducting, to tuck it up in the joist bays, and I discovered that the exhaust muffler doesn't really do anything, now that an intake muffler is in place. The bulk of the noise seems to be generated at the intake; once you silence that, you're golden.

So I'm leaving the intake muffler in place, and using the second muffler to quiet the intake of the inline fan I'm about to mount to cool the HPS lighting.

Live and learn. :smokin: