If particle board or MDF, then they might just be disintegrating.

also when you look under the furnace vent check out the subfloor..... you could have particle board under there.

And an overflow might easily occur while your attention is elsewhere.Laminate floors:If a laminate wood floor is installed, there are two ways to damage them 1) scratch them by dragging furniture and other hard things across the floor or 2) allowing spilled water to sit in a puddle which causes the particle board backing to warp.

3/4 inch plywood secured by carriage bolts going through 2x4 wood stretched across the opening on the inside twice.Chalk the outside and paint the same color as the foundation.Don't cheapen the process, don't use particle board or OSB, don't use screws, and don't use 2x2s or 2x4s

With all the pollen and other particles in the air outside there is no way to prove it's from inside the house. 

Opening a unit and dumping out debris makes no sense, as particles become airborne.Another tip, don't use a shop vac for cleaning out fireplace ash... there are special vacs to that.

You know, misaligned particle board/paper cabinets, dust and dirt in the floor finishes, caulking filling 2 inch gaps in the vinyl siding and blackjack all over the roof where the flashing should be...I call it Menarded

True, but the boxes are really cheap particle board.

I'm looking for ready to assemble (RTA) that do not have any particle board or OSB.Found RTACabinets.com which seems interesting but I'd like to look at some in person if possible, maybe even LA County.Current quote from HD (Home Depot) for their ready made in inventory cabinets is $2600, those are particle board low grade cabinets.I'm going to bet Kevin Fox replies in this thread.

Lint will make it by the 1st screen and build up from very small particles that were not caught.