Well that idea goes out the window. Check the vacuum line running to your BOV. Pull it off, and plug it with your finger before starting. If you pull your finger off, and the engine sounds exactly the same, you have a leak between the BOV and the other end of that line. Honestly, at this point I can't do much more than think of things that MIGHT cause this. Roll the lines coming off the inlet and checking for cracks would be the final thing I would do before sleeping on it. This is quite the predicament.