Mindy...my knees have always cracked/popped a bit too. Not always when I bend them, just sometimes. I asked my Chiropractor if it was bad and he said "No, as long as there is no pain". Sometimes your body just has a way of adjusting itself I think...
I get the poppin' too. Not all the time, ever so often. Sometimes I can just be sitting there & will feel the need for it to pop, weird. No pain though.
What is kind of gross is when I get a popping in my hip while doing certain ab exercises.
Mine grind / crunch... I hate going upstairs sometimes and it is loud enough for others to hear... (in a quiet stairway of course).. My sports med doc said there wasnt a whole lot to do about it either as long as there is no pain... just gives me the willies sometimes....