Just signed up. I'm Rob, the owner of said P.I.T.A. sub. It's loud and clean, no distortion, just puts out a random pop at around 40hz. Been doin this stuff for years and never seen this before. Almost sounds like the coil is bottoming, but it'll just do it once, not the whole time it's at freq. 30hz is clean and will go full excursion cleanly. Just around 40 hz has a random pop. No bass boost on,(amp or hu). No other issues. Lost on this one