A Small Press on the Accelerator (1,000 - 2,000 RPM) for a couple of seconds Produces a Short Hiss (Sound of Sipping Tea, Coffee). I've done this repeatedly for a few times, and the same sound occurs. Is this something to be concerned about. I have a couple of fault codes pertaining to the Catalytic Converter below threshold, but the O2 sensors appear fine. I have two misfires; the other four spark plugs / coils are intact.