Thanks for all the great ideas and help. Really appreciate everyone taking the time to post. I tried to respond to each of you folks below.... Keep 'em coming! I have to put off checking this out until the weekend but will be sure and post any new info or cause that I find.
Bob
send small thin person to check crawl space.ny gtter or downspoy issues in that area? hows crawlspace ventilation?
** I'm in dry S Calif - very little rain, good drainage, etc. Crawlspace ventilation is good all around
Any plants in the room?
** None in the house or near windows/doors
What kind of heat? If hot air, all parts of the house should be equally bad. If not hot air, are there any connections to the outside, like a stove hood vent or holes in the wall where pipes or electric outlets go thru?
** Gas heat, but furnace gas supply valve turned off since Feb 2010 due to warm winters. No circulation room to room to speak of. Problem is strictly in one part of the house.
One possibility is mold. They sell DIY mold test kits that you leave exposed to the air then send in to be tested. I think I saw them at HD or Lowes. That might be a cheap first step. Don't know how well they work, accuracy, etc. I'm sure some googling for air testing will produce results. Also must be some outfits that do more extensive testing in the yellow pages.
** Sounds like a good idea - has anyone ever tried these? I'm always suspicious that these type of tests would always pick up enough stray spores show a positive. Or if it was negative, it could be upwind from mold and not pick it up.
forgot to mention. the corner 'may' be only an 'accumulation' area. the true source could be elsewhere.
** Good point - will check out behind furniture, etc
Plus, since you have alergies anyway, get an electrostatic very slow air flow air cleaner and place in that corner, The air cleaner will remove irriants and the slight amount of ozone may be enough to kill the source.. Anway, you need one ayway. Oreck makes a small portable [expensive!] electrostatic air cleaner that's easy to live with.
** Allergies are only in June-July. Never this time of the year. Smell is definitely not any type of pollen, and has been here at least since December.