Ok so I just bought a brand new WRX, I'm at about 450 miles now and have been taking it real easy keeping it under 4K everywhere I drive. Well I was in traffic yesterday coasting in fifth gear at around 2K in the far right lane and traffic was merging, long story short to avert a collision I downshifted into 3 to speed up gave it a good rev match and released clutch, "it didn't jolt me forward or put me in my seat belt" so I know I matched it right- well after clutch was fully engaged and beginning acceleration I got a very loud POP that sounded like it came from under the car and felt it too. It's scared the crap out of me because I'm not sure if it was just back pressure or something mechanical.. Any idea what this could have been? I'm hoping it's back pressure but I've never heard of a pop accruing in your down pipe or before exiting your exuast, I had a turbo charged , 5 speed Cobalt before I got my WRX and it would pop all the time reving up to 6k and pushing in the clutch, but this seemed different.. any thoughts? I'm kinda Stressin it's brand spanking new.