'05 lexus rx330 ash dust on dashboard

Hi, I wonder if anybody has the same problem I'm having on my RX330. I keep getting a lot
of ash like dust on my dash that doesn't go away. I used a leaf blower to thoroughly clean the
area where cabin filter is inserted then replaced the cabin filter but dust still persistent. In a week looks like dandruff...Any ideas what's causing these. Also went to Longo about the problem
and suggested it's coming from the outside where I'm driving...isn't that the cabin filter's job??
 
Please help....

its the heater core.... there is a bulletin for an updated part number. take it in.