Unknown floating substances in culture flask - (Jun/29/2012 )

hi all,

I feel really frustrated with these strange things in my culture flasks. They are floating in the culture medium. Their sizes are comparable with my cancer cells(PC-3 and A549). They reappear even though I wash the cells many times before re-adding the medium. And it seems that there will be more and more such floating things a few days later. Are my cells contaminated??

These are dead/dying cells. ANy population of cells will have a few.