My 2014 STi came with the optional SPT catback system. My car is currently 100% stock. ~6100 miles on the clock. I've noticed recently that if I'm running in S#, and I do a hard pull 1st through 3rd, I'll get a few rumbles/booms in the exhaust. The engine is completely warm beforehand; and by warm I mean 10+ mins of driving, well after coolant reaches operating temps. Could it be the warmer weather? I haven't changed anything; still running 93 from QuikTrip. Anyone else get after-fire/backfire? It's not the higher-pitched "popping" that you sometimes hear in aftermarket exhausts. It's more like a rumble, and you can feel it resonate through the body of the car. Imagine the sound you hear when you light a gas grill/furnace; that low "FWOOMP", quasi "explosion" from the gas rapidly igniting in a confined space. Anyway, I'm just wondering if anyone else has this happening. I was thinking about going with a Cobb AP but I still haven't decided/saved enough money yet.