Wow. Thanks for all the replies. Here goes: the exhaust looks OK, no cracks, everything tight and baffles look ok too. There is no tuner or fuel remap. So I'm hoping I just got some bad gas. I had to stop in the middle of nowhere at a little store. And, yes I have opened the garage door with the engine running! I asked the dealer's service guys if they had done anything that would affect the exhaust and they assurred me thy had not. The real problem is I liked the sound better before.