I've been working through a few things on my b15 SER Spec V lately and I noticed a completely random rattle/vibration coming from the exhaust area. Last night I pulled the muffler down (has a broken hanger) then noticed the heat shield for the fuel tank was loose. I tightened it up and left the muffler off to re-weld that hanger back on later and since then I can only hear it better now. Upon cold start I can hear a loud vibration maybe 2 or 3 times then it stops, but while cruising in the rpm range of 2000-3000 I can hear a flappy tappy (only way to really describe it lol) sound specifically through the exhaust. Inside the engine bay during different rpm it sounds like a healthy engine. I'm concerned if this could be caused by the pre-cat, it does have a brand new one but it's still factory (CA smog...). The sound doesn't continue around 4000+ rpm. I've checked for oil consumption, there's none, I've just replaced both cam/crank position sensors, all recalls were handled (checked vin). The head gasket is new, intake manifold has been pulled apart (some unimportant bolts are missing or mixmatched) which could mean the butterflies were fixed. An important thing to note is that the previous owner hit a curb, the front passenger side wheel has minor damage to the paint and power steering pulley is wobbling, along with a bad link bushing but there are no signs of catastrophic damage to anything else on that side.