I heard a pop noise when I turned on my A/C yesterday. Then noticed a small amount of dirty looking spongy material inside A/C vents. Worked this spongy foam out of vents with a bent paperclip. A/C made an increasing roaring noise as I upped the A/C fan speed.
This morning the roar was gone. A/C seems to be cooling OK considering the plus-100 degree weather in Dallas these days.
What is the model year of your Avalon?
Is it equipped with a Cabin Air Filter?
If so, when was the last time that this filter was changed?
If your car has one of those filters, and if it was really clogged with dust, pollen, insects, leaf fragments, and other debris, it could have gotten to the point where the filtering medium just broke apart. Check your Owner’s Manual for the location of your Cabin Air Filter (probably accessed by removing the glove box), and check the filter.
If I am correct in my diagnosis, you will likely find just the frame for the filter, with little or no filtering medium left. You could just leave things as they are, but if you or any of your frequent passengers suffer from seasonal allergies, you really should replace the filter and then stay on a schedule of replacing it once a year.
That might have been a piece of the gasket that seals the vent registers to the duct-work.
1999 Avalon.
I do not believe it has a Cabin filter. Looking this up on the Internet I think this was a new part for 2000 and higher years. The spongy foam does look like it could be from some type of filter though.