HELP with cell lysis for DNA assay - Something is floating in my lysate solution!!! (Feb/15/2010 )

I am harvesting pulmonary epithelial cells (IB3-1) in NP-40 lysis buffer + protease inhibitor cocktail. After adding the NP-40 + P. Inhibitor solution to the living cell monolayer (in a 100mm cell culture plate), scraping them, and collecting them in a centrifuge tube; a large aggregate mass of something forms and will not break up. Does anyone know what this aggregate mass is??? All of the cells have lysed so it's not cells reattaching to each other. Any help would be greatly appreciated.

probably protein bound to DNA.