I sometimes drive by my local sewage treatment plant in my 17 MDX. I would always make sure I was on "Recirculate" when I'd go by to stop the smell (mostly) from coming in. Lately, even when on "Recirculate", I really smell the odors. Enough to make me question the operation of the inside/outside diverter valve. I have sped up the fan, muted the radio, and flipped between Outside and recirc and can hear a SLIGHT difference in the sound of the fan. The difference in sound used to be more pronounced in past times when I would switch back and forth. Anyone have any suggestions as to properly check this matter out? Has someone out there had this same issue?