What cause a tight knees while exercising?

when i do squats and stuff my knees crack sometimes, and after an hour of cardio and weight lifting my knees be aware of tight. what's this mean?What cause a tight knees while exercising?
It's possible that you hold Arthritis if I walk too much my not here knee give me a fit and I have to sit down for a while.
That is inherent unless you have arthritis.The tightness of the knees is from the muscle workout and that's majority too.
is it one or both knees?
if it's one, it could be due to overuse...leading to the synovial fluid contained by the joint getting slender

solar dermatitis